Yahya related to me from Malik from Yahya ibn Said that a manasked Said ibn al-Musayyab, "I pray in my house, and then I come tothe mosque and find the imam praying. Should I pray with him?" Saidsaid, "Yes," and the man said, "Which of them is my prayer?" Saidsaid, "Are you the one to decide that? That is up to Allah."
App reference: Book 8, Hadith 11
USC-MSA web (English) reference: Book 8, Hadith 11
Arabic reference: Book 8, Hadith 300