1. Abu Bakr was not appointed as the successor [Khalifah].

Sahih-ul-Bukhari, Hadith No. 7218, Kitab-ul-Ahkam, Bab-ul-Istikhlaf:

Abdullah son of Umar narrates that Umar was asked: “Will you not appoint a successor?” Umar replied: “If I appoint a successor, someone better than me has already appointed [me]: Abu Bakr and if I refrain from doing so, someone better than me has already refrained from doing so: The Messenger of God (s.).”

حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، أَخْبَرَنَا سُفْيَانُ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ قِيلَ لِعُمَرَ أَلاَ تَسْتَخْلِفُ قَالَ إِنْ أَسْتَخْلِفْ فَقَدِ اسْتَخْلَفَ مَنْ هُوَ خَيْرٌ مِنِّي أَبُو بَكْرٍ، وَإِنْ أَتْرُكْ فَقَدْ تَرَكَ مَنْ هُوَ خَيْرٌ مِنِّي رَسُولُ اللَّهِ صلى الله عليه وسلم فَأَثْنَوْا عَلَيْهِ فَقَالَ رَاغِبٌ رَاهِبٌ، وَدِدْتُ أَنِّي نَجَوْتُ مِنْهَا كَفَافًا لاَ لِي وَلاَ عَلَىَّ لاَ أَتَحَمَّلُهَا حَيًّا وَمَيِّتًا‏.‏

2. The successor [Khalifah] is appointed by Allah according to the Qur’an.

Sura No. 24, An-Nur, verse 55:

“God promised those of you who believe and act righteously that He will appoint for them successors on the earth, just as He appointed successors for those before them.”

وَعَدَ اللَّهُ الَّذِينَ آمَنُوا مِنكُمْ وَعَمِلُوا الصَّالِحَاتِ لَيَسْتَخْلِفَنَّهُمْ فِي الْأَرْضِ كَمَا اسْتَخْلَفَ الَّذِينَ مِن قَبْلِهِمْ

Before them, the successors were not elected by humans, but appointed by Allah. Examples are Adam (Sura 2:30), Dawud (Sura 38:26), and Harun through Musa (Sura 7:142). Allah promises that He will do this as He did with previous nations. This does not apply to Abu Bakr because he was never appointed as a successor by the Prophet but instead was voted upon.

3. The Prophet appointed a successor [khalifah]

The Book of al-Musnad by the Sunni scholar Ahmad ibn Hanbal, Volume 5, Page 27, Hadith No. 3062, Musnad Ibn Abbas:

Abdullah ibn Abbas narrates that the Prophet (s.) said to Ali: “Are you not satisfied that you have a position with me that Harun has with Musa, except that you are not a prophet? It shall not be, that I will leave, unless you are my successor.”

حدثنا يي بن حاد حدثنا أبو عوانة حدثنا أبو بلج حدثنا عمرو بن ميمون عن ابن عباس عن رسول الله صلى الله عليه وسلم أنه لعلي رضي الله عنه: أما ترضى أن تكون مني بمنزلة هارون من موسى إلا أنك لست بنبي إنه لا ينبغي أن أذهب إلا وأنت خليفتي

The Sunni scholar Ahmad Muhammad Shakir classifies Hadith No. 3062 on page 25 as follows:

“Its chain of transmission is authentic [Sahih].”

إسناده صحيح

The book al-Bidayah wa n-Nihayah by the Sunni scholar Ibn Kathir, volume 11, page 44-45, the year Forty after the Prophet’s emigration, chapter on the merits of Ali ibn Abi Talib:

Abdullah ibn Abbas narrates that the Prophet (s.) said to Ali: “Are you not satisfied that you have a position with me that Harun has with Musa, except that you are not a prophet? It shall not be, that I leave, unless you are my successor.”

فقال المام أحد ثنا يي بن حاد ثنا أبو عوانة ثنا أبو بلج ثنا عمرو بن ميمون عن رسول الله صلى الله عليه وسلم أنه قال لعلي: أما ترضى أن تكون مني  بمنزلة هارون من موسى إلا أنك لست بنبي إنه لا ينبغي أن أذهب إلا وأنت خليفتي

The Sunni scholar Abdullah ibn Abdi l-Muhsin at-Turki classifies the hadith on page 43 as follows:

“Its chain of transmission is authentic [Sahih].”

إسناده صحيح

The book al-Mustadrak by the Sunni scholar Al-Hakim An-Naisaburi, volume 3, page 144, hadith no. 4652, Ma’rifat-us-Sahabah:

Abdullah ibn Abbas narrates that the Prophet (s.) said to Ali: “Are you not satisfied that you have a position with me that Harun has with Musa, except that after me none is a prophet? It shall not be, that I leave, except that you are my successor.”

أخبرنا أبو بكر أحمد بن جعفر بن حمدان القطيعي ببغداد من أصل كتابه ثنا عبد الله بن أحمد بن حنبل حدثني أبي ثنا يحيى بن حماد ثنا أبو عوانة ثنا أبو بلج ثنا عمرو بن ميمون عن عبد الله بن عباس عن رسول الله صلى الله عليه وسلم أنه قال لعلي رضي الله عنه: أما ترضى أن تكون مني  بمنزلة هارون من موسى إلا أنك لست بنبي إنه لا ينبغي أن أذهب إلا وأنت خليفتي

The author of the book, Al-Hakim an-Naisaburi, classifies hadith number 4652 on page 144 as follows:

“This one is a hadith with a chain that is authentic [Sahih].”

هذا حديث صحيح السناد

The Sunni scholar Muhammad ibn Ahmad adh-Dhahabi classifies Hadith No. 4652 on page 143 as follows:

“Authentic [Sahih].”

صحيح

The book as-Sunnah by Sunni scholar Abu Bakr ibn Abi Asim, page 799 – 800, Hadith No. 1222, Bab Fi Dhikr Khilafat Ali ibn Abi Talib:

Abdullah ibn Abbas narrates that the Prophet (s.) said to Ali: “You have the position with me that Harun has with Musa, except that you are not a prophet. It shall not be, that I leave, except that you are my successor to every believer after me.”

ثنا محمد بن المثنى، حدثنا يحيى بن حماد عن أبي عوانة عن يحيى بن سليم أبي بلج عن عمرو بن ميمون عن ابن عباس قال قال رسول الله صلى الله عليه وسلم لعلي: أنت مني  بمنزلة هارون من موسى إلا أنك لست نبيا إنه لا ينبغي أن أذهب إلا وأنت خليفتي في كل موْمن من بعدي

The Sunni scholar Muhammad Nasir-ud-Din al-Albani classifies Hadith No. 1222 on page 800 as follows:

“Its chain of transmission is good [Hasan].”

إسناده حسن

The book al-Mustadrak by the Sunni scholar al-Hakim an- Naisaburi, volume 3, page 154, hadith no. 4686, Kitab: Ma’rifat-us-Sahabah:

عن حيان الأسدي سمعت عليا يقول : قال لي رسول الله صلى الله عليه و سلم إن الأمة ستغدر بك بعدي وأنت تعيش على ملتي وتقتل على سنتي من أحبك أحبني ومن أبغضك أبغضني و إن هذه ستخضب من هذا يعني لحيته من رأسه

Ali ibn Abi Talib narrates that the Prophet (s.) said to him: “The Ummah will betray you after me and you live by my faith and they will kill you, while you adhere to my Sunnah. Whoever loves you loves me and whoever hates you, hates me and therefore this one will be colored.” By which he meant his beard from his head [Ali’s beard will turn red from blood when he is killed]

The author of the book, al-Hakim an-Naisaburi, classifies hadith no.4686 on page 154 as follows:

„Authentic [Sahih].”

صحيح

The Sunni scholar Muhammad ibn Ahmad adh-Dhahabi classifies hadith no. 4686 on page 153 as follows:

“Authentic [Sahih].”

صحيح

The book al-Mustadrak by the Sunni scholar al-Hakim an Naisaburi, volume 1, page 217, hadith no. 441, Kitab-ul-Ilm:

Abu Hurairah narrates that the Prophet (s.) said: “The Jews split into 71 groups, the Nasara split into 72 groups and my Ummah will split into 73 groups.”

أخبرنا أحمد بن محمد بن سلمة العنزي ثنا عثمان بن سعيد الدارمي ثنا عمرو بن عون ووهب بن بقية الواسطيان قالا: ثنا خالد بن عبد الله عن محمد بن عمرو عن أبي سلمة عن أبي هريرة قال قال رسول الله صلى الله عليه وآله افترقت اليهود على احدى أو اثنتين وسبعين فرقة وافترقت النصارى على احدى أو اثنتين وسبعين فرقة وتفترق أمتي على ثلاث وسبعين فرقة

Abu Hurairah narrates that the Prophet (s.) said: “The Jews split into 71 groups, the Nasara split into 72 groups and my Ummah will  split into 73 groups.”

The author of the book, al-Hakim an-Naisaburi, classifies hadith No. 441 on page 217 as follows:

“This is a hadith that is authentic [Sahih] according to Muslim.”

هذا حديث صحيح على شرط مسلم

The Sunni scholar Muhammad ibn Ahmad adh-Dhahabi classifies hadith no. 441 on page 217 as follows:

“It fulfills the condition of Muslim (author of Sahih Muslim).”

على شرط مسلم