Abu Tufayl reported,

Ali, may Allah be pleased with him, gathered the people in the open courtyard and said to them, "I implore by Allah every Muslim man who heard the Messenger of Allah ﷺ speak on the Day of Ghadir Khumm to stand and bear witness to what he heard."Thirty men stood up. Abu Naeem said that many people stood up and testified that the Messenger of Allah ﷺ took Ali by the hand and said to the people, "Do you know that I have a greater claim over the believers than they have over themselves?"They replied, "Yes, Messenger of Allah."He said, "Whoever takes me as his master, this man is his master. O Allah, befriend whoever befriends him and oppose whoever opposes him."The narrator said, "I left with something troubling me, then I met Zayd bin Arqam and said to him, 'I heard Ali, may Allah be pleased with him, say such and such.'"Zayd replied, "What is there to deny? I myself heard the Messenger of Allah ﷺ say that about him."

Ahmad 19302

Sahih

حدثنا حسين بن محمد وأبو نعيم المعنى قالا ثنا فطر

عن أبي الطفيل قال

جمع علي رضي الله تعالى عنه الناس في الرحبة ثم قال لهم أنشد الله كل امرئ مسلم سمع رسول الله ﷺ يقول يوم غدير خم ما سمع لما قام فقام ثلاثون من الناس وقال أبو نعيم فقام ناس كثير فشهدوا حين أخذه بيده فقال للناس أتعلمون أني أولى بالمؤمنين من أنفسهم قالوا نعم يا رسول الله قال من كنت مولاه فهذا مولاه اللهم وال من والاه وعاد من عاداه قال فخرجت وكأن في نفسي شيئا فلقيت زيد بن أرقم فقلت له إني سمعت عليا رضي الله تعالى عنه يقول كذا وكذا قال فما تنكر قد سمعت رسول الله ﷺ يقول ذلك له

أحمد 19302صحيح
Contents
Reference
Commentary
Ayat
Collection
Musnad Ahmad
Book
Zayd bin Arqam
Numbering
Darussalam 19302
Ahmad 19302