Musannaf Ibn Abi Shaybah 4209 — The multiplied reward recorded

Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: "When a man joins the congregation while the people are sitting at the end of the prayer, he has obtained a double reward. And if he joins the congregation after the imam has given the salam but the people have not yet dispersed, he still obtains a double reward."
Ata said: "It used to be said: When a person leaves his house intending to join the congregation, he has obtained a double reward, even if he does not reach the congregation."