Yahya related to me from Malik from Afif as-Sahmi that a man fromthe tribe of Bani Asad asked Abu Ayyub al-Ansari. "Sometimes I pray inmy 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 someone who does so has the reward of the group, or the equivalent of thereward of the group."
App reference: Book 8, Hadith 12
USC-MSA web (English) reference: Book 8, Hadith 12
Arabic reference: Book 8, Hadith 301