He said, "Messenger of Allah, do not say ameen before me."
حدثنا إسحق بن إبراهيم بن راهويه أخبرنا وكيع عن سفيان عن عاصم عن أبي عثمان
أنه قال يا رسول الله لا تسبقني بآمين
No references are available.
Sourcing, sahih. Ahmad reported it, 12/6, 15, from the hadith of Aasim al-Ahwal, through this same chain, and Hakim graded it sahih according to the standard of the two Shaikhs, 1/219, and Dhahabi agreed with him.