Muhammad ibn Uthman reported, that Imam Al-Mahdi (a.) said:“As for the occurring events, return therein to the narrators of our saying, for they are my proof against you and I am the proof of God against you.” [Al-Ghaibah of At-Tusi, page 184]

جماعة عن جعفر بن محمد بن قولويه وأبي غالب الزراري وغيرهما عن محمد بن يعقوب الكليني عن إسحاق بن يعقوب عن محمد بن عثمان العمري عن الإمام المهدي عليه السلام قال: وأما الحوادث الواقعة فارجعوا فيها إلى رواة حديثنا فإنهم حجتي عليكم وأنا حجة الله عليكم

There are some problems with using this tradition as evidence for taqlid.

[1.] The Imam used the word “narrator” of the sayings and not “jurists”.

[2.] Grand Usuli scholars considered this tradition weak, so it cannot be used as evidence for taqlid.

Al-Khui:

,,This letter was narrated by three people, two of them are weak because their trustworthiness has not been proven, so this narration is not trustworthy. The tradition calls for us to turn to the narrators of the sayings.” [Tanqih al-Urwat al-Uthqa, Vol. 1, page 302]

Al-Khumaini:

,,The tradition is weak. The tradition written down by Ishaq ibn Yaqub has not been transmitted to us, so we do not know the context and what the Imam (a) said.” [al-Ijtihad wa Al-Taqlid, pages 99-100]