Ali appointed Abu Masud to lead the people in his absence. Abu Masud went out on the day of Eid and said, "People, it is not from the Sunnah to pray before the imam."
أخبرنا إسحق بن منصور قال أنبأنا عبد الرحمن عن سفيان عن الأشعث عن الأسود بن هلال
أن عليا استخلف أبا مسعود على الناس فخرج يوم عيد فقال يا أيها الناس إنه ليس من السنة أن يصلى قبل الإمام
No references are available.
[Hasan] It is in Kubra, no. 1761, and the basic hadith has corroborating witnesses. Sufyan Thawri, Tabarani, from Ashath bin, and he stated it clearly in another hadith (mentioned earlier, no. 1531). Shubah followed him, as reported by Tabarani, from, he used the indirect form "ana" here, from Sulaym, with the same wording, but he omitted Thalaba bin Zahdam, Kubra, 17/248, no. 692.