I came to Umm Kulthum, the daughter of Ali, with something from the charity, but she returned it and said, "A freed slave of the Prophet ﷺ named Mahran told me that the Messenger of Allah ﷺ said, 'We, the family of Muhammad, are not permitted to accept charity, and the freed slave of a people is one of them.'"
حدثنا وكيع حدثنا سفيان
أتيت أم كلثوم ابنة علي بشيء من الصدقة فردتها وقالت حدثني مولى للنبي ﷺ يقال له مهران أن رسول الله ﷺ قال إنا آل محمد لا تحل لنا الصدقة ومولى القوم منهم
No references are available.
Its chain of transmission is sahih. Ata bin Saaib became confused in his later years, but Sufyan narrated from him before this confusion set in. The hadith has come before many times. See 7744 and 1723.