Muwatta Malik #300

Yahya related to me from Malik from Afif as-Sahmi that a man from the tribe of Bani Asad asked Abu Ayyub al-Ansari. "Sometimes I pray in my house, and then come to the mosque and find the imam praying. Should I pray with him?" Abu Ayyub said, "Yes, pray with him, for some one who does so has the reward of the group, or the equivalent of the reward of the group."