Qur’an:

“O you who believe, when you walk about in the land in the way of God, establish the situation clearly and do not say to him, who offers you peace: “You are not a believer!” In seeking the goods of this worldly life. Surely God creates many opportunities, to obtain the booty. That is how you were before, when God did you a favour. So establish the situation clearly. God has knowledge of what you do.” [An-Nisa’ 4:94]

يا أيها الذين آمنوا إذا ضربتم في سبيل الله فتبينوا ولا تقولوا لمن ألقى إليكم السلام لست مؤمنا تبتغون عرض الحياة الدنيا فعند الله مغانم كثيرة كذلك كنتم من قبل فمن الله عليكم فتبينوا إن الله كان بما تعملون خبيرا

Sunnah:

Ali Ibn Ibrahim Al-Qummi writes: “This verse was revealed, when the Prophet Muhammad (s.) returned from his campaign in Khaibar and sent Usamah Ibn Zaid with a horse to some villages of the Jews in the direction of Fadak, so that he might call them to submission to God. Among the Jews was a man, who was called Mardas Ibn Nahik Al-Fadaki in some villages and when he noticed the horse of the Messenger (s.), he gathered his people and his wealth and set off towards the mountains. When he met him, he said: “I bear witness that none is worthy of worship except God and that Muhammad is the Messenger of God.” But when he passed by Usamah ibn Zaid, he attacked him and murdered him. When Usamah said to the Messenger (s.) he told him about it. Thereupon the Prophet (s.) said to him: “You have murdered a man, who testified, that none is worthy of worship except God and that I am the Messenger of God?” Usamah said: “O Messenger of God, surely he only said that to escape from being killed!” The Prophet (s.) said: “Have you ripped his heart out of his chest and accepted, what he said with his tongue and learned what was inside him?” Thereupon he swore, not to murder anyone, who testifies that none is worthy of worship except God and Muhammad is the Messenger of God, but he would turn away from the Commander of the Believers (a.) in his wars and God therefore revealed this verse (4:94): “And do not say to him who offers you the peace: ‘”You are not a believer!” [Tafsir Al-Qummi, Volume 1 page 148 – 149]

قال شيخ الإسلام القمي رضي الله عنه: فإنها نزلت لما رجع رسول الله صلى الله عليه وآله من غزوة خيبر وبعث أسامة بن زيد في خيل إلى بعض قرى اليهود في ناحية فدك ليدعوهم إلى الاسلام، وكان رجل من اليهود يقال له مرداس بن نهيك الفدكى في بعض القرى فلما أحس بخيل رسول الله صلى الله عليه وآله جمع أهله وماله وصار في ناحية الجبل فاقبل يقول اشهد ان لا اله إلا الله وان محمدا رسول الله صلى الله عليه وآله، فمر بأسامة بن زيد فطعنه فقتله، فلما رجع إلى رسول الله صلى الله عليه وآله اخبر بذلك فقال له رسول الله صلى الله عليه وآله قتلت رجلا شهد أن لا إله إلا الله واني رسول الله فقال يا رسول الله إنما قال تعوذا من القتل فقال رسول الله صلى الله عليه وآله فلا شققت الغطاء عن قبله ولا ما قال بلسانه قبلت ولا ما كان في نفسه علمت فحلف بعد ذلك أنه لا يقتل أحدا شهد ان لا إله إلا الله وأن محمدا رسول الله صلى الله عليه وآله، فتخلف عن أمير المؤمنين عليه السلام في حروبه، وأنزل الله في ذلك ولا تقولوا لمن القى إليكم السلم لست مؤمنا

Muhammad ibn Makki reported that Imam As-Sadiq (a.) said: “Modesty consists in, that you are satisfied with sitting together, even without your honour and you give the greeting of peace, to the one whom you meet and you refrain from quarrelling, even if you were in the right. The head of goodness is humility.” [Mawsu’at Ahadith Ahl Al-Bait by An-Najafi, Volume 2 page 253]

عن محمد بن مكي عن الإمام الصادق عليه السلام قال: التواضع أن ترضى من المجلس بدون شرفك وان تسلم على من لاقيت وأن تترك المراء وإن كنت محقا ورأس الخير التواضع

The followers of Umar mention something similar.

Evidence:

Abu Zibyan reported that Usamah ibn Zaid said: “Prophet Muhammad (s) sent us to Al-Huraqah, which belonged to the tribe of Juhainah and when we reached the people in the morning, we defeated them. I and one of the helpers came across a man of theirs and when we captured him, he said: “None is worthy of worship except God.” So the helper left him alone, but I stabbed him with my spear until I finally murdered him. When we returned, the Messenger (s.) heard about it and said to me: “O Usamah, you murder him after he testified that none is worthy of worship except God?” I said: “O Messenger of God, he only did it to save his life!” He said: “You murder him after he testified that none is worthy of worship except God?” The Prophet (s.) did not stop repeating it until I wished I had never embraced Islam before that day.” [Sahih Al-Bukhari, Hadith 6478]

حدثنا عمرو بن زرارة حدثنا هشيم حدثنا حصين حدثنا أبو ظبيان قال سمعت أسامة بن زيد بن حارثة رضي الله عنهما يحدث قال بعثنا رسول الله صلى الله عليه وسلم إلى الحرقة من جهينة قال فصبحنا القوم فهزمناهم قال ولحقت أنا ورجل من الأنصار رجلا منهم قال فلما غشيناه قال لا إله إلا الله قال فكف عنه الأنصاري فطعنته برمحي حتى قتلته قال فلما قدمنا بلغ ذلك النبي صلى الله عليه وسلم قال فقال لي يا أسامة أقتلته بعد ما قال لا إله إلا الله قال قلت يا رسول الله إنما كان متعوذا قال أقتلته بعد ما قال لا إله إلا الله قال فما زال يكررها علي حتى تمنيت أني لم أكن أسلمت قبل ذلك اليوم

Asbat reported that Isma’il Ibn Abd Ar-Rahman As-Suddi mentioned the verse: “And say not to him who offers you the peace: “You are not a believer!” While seeking the goods of this worldly life.” (4:94) He said: “Prophet Muhammad (s) sent Usamah Ibn Zaid with a military unit to the sons of Damrah. Thereupon they met a man named Mardas Ibn Nahik who had wealth and a red camel with him. After seeing them, he took refuge in the cave of a mountain, whereupon Usamah followed him. When Mardas reached the cave, he placed his wealth therein and then came to them and said: “Peace be upon you, I bear witness that none is worthy of worship except God and that Muhammad is the Messenger of God!” Usamah then took him as a prisoner and murdered him, to enrich himself with his camel and wealth. When the Prophet (s.) sent Usamah, he wished him to return in good spirits and asked his companions about him. When they returned, he did not ask them about him. He caused the people to talk to the Prophet (s.) and they said: “O Messenger of God, if only you had seen Usamah when a man met him and said: “I bear witness that none is worthy of worship except God and that Muhammad is the Messenger of God!” And he then took him as a prisoner and murdered him!” He turned away from them and when they increased their complaints to him, he raised his head to Usamah and said: “How can you, although he testifies that none is worthy of worship except God?” Usamah said: “O Messenger of God, he only testified to this to save his life by it.” The Prophet (s) said to him: “Did you pull his heart out of his chest and look into it?” Usamah said: “O Messenger of God, his heart is only a part of his body.” Thereupon God revealed this report and notified the Prophet (s.) that he murdered him for his camel and wealth. For this reason it is said: “In seeking the goods of this worldly life.” (4:94) When he said: “From God comes that, which is incumbent upon you. He says: “God turns to you.” Usamah swore not to murder any man who testifies that none is worthy of worship except God. After that man, nothing concerned him from the Messenger (s.) regarding that.” [Ad-Durr-ul-Manthur of As-Suyuti, Volume 3 page 203]

حدثنا محمد بن جرير قال حدثنا محمد بن الحسين قال: ثنا أحمد بن المفضل قال ثنا أسباط عن السدي: يأيها ٱلذين ءامنوا إذا ضربتم فى سبيل ٱلله فتبينوا ولا تقولوا لمن ألقى إليكم ٱلسلم لست مؤمنا تبتغون عرض ٱلحيوة ٱلدنيا الآية. قال: بعث رسول الله صلى الله عليه وسلم سرية عليها أسامة ابن زيد إلى بني ضمرة, فلقوا رجلا منهم يدعى مرداس بن نهيك معه غنيمة له وجمل أحمر, فلما رآهم أوى إلى كهف جبل, واتبعه أسامة, فلما بلغ مرداس الكهف وضع فيه غنمه, ثم أقبل إليهم فقال: السلام عليكم أشهد أن لا إله إلا الله وأن محمدا رسول الله! فشد عليه أسامة فقتله من أجل جمله وغنيمته. وكان النبي صلى الله عليه وسلم إذا بعث أسامة أحب أن يثني عليه خيرا, ويسأل عنه أصحابه, فلما رجعوا لم يسألهم عنه فجعل القوم يحدثون النبي صلى الله عليه وسلم ويقولون: يا رسول الله لو رأيت أسامة ولقيه رجل فقال الرجل: لا إله إلا الله محمد رسول الله, فشد عليه فقتله! وهو معرض عنهم. فلما أكثروا عليه رفع رأسه إلى أسامة فقال: كيف أنت ولا إله إلا الله؟ قال: يا رسول الله إنما قالها متعوذا, تعوذ بها. فقال له رسول الله صلى الله عليه وسلم: هلا شققت عن قلبه فنظرت إليه؟ قال: يا رسول الله إنما قلبه بضعة من جسده. فأنزل الله عز وجل خبر هذا, وأخبره إنما قتله من أجل جمله وغنمه, فذلك حين يقول: تبتغون عرض ٱلحيوة ٱلدنيا فلما بلغ: فمن ٱلله عليكم يقول: فتاب الله عليكم, فحلف أسامة أن لا يقاتل رجلا يقول لا إله إلا الله بعد ذلك الرجل وما لقي من رسول الله صلى الله عليه وسلم فيه