Musannaf Ibn Abi Shaybah

Hazrat Abu Huraira says that when a person joined the congregation while the people were sitting at the end of the prayer, he received double reward. If he joined the congregation after the Imam had said the salam, but the people had not yet dispersed, he still received double reward. Hazrat Ata says that it was said that when a person left his house with the intention of joining the congregation, he received double reward even if he could not reach the congregation.

Hazrat Abdullah says that whoever reaches the Tashahhud has attained double reward.

Hazrat Abu Salamah says that whoever leaves the house before the Imam finishes the salam will receive double the reward.