Musannaf Ibn Abi Shaybah 4639 — A man who misses part of the imam's

Uqbah bin Abi al-Ayzar said: I asked Ibrahim about a person who joins the imam in prayer after missing a rak'ah, and the imam makes a lapse: what should he do? He said: "Since he has joined the imam in prayer, he should do what the imam does."