Muwatta Malik

Yahya related to me from Malik from Yahya ibn Said that a man asked Said ibn al-Musayyab, ""I pray in my house, and then I come to the mosque and find the imam praying. Should I pray with him?"" Said said, ""Yes,"" and the man said, ""Which of them is my prayer?"" Said said, ""Are you the one to decide that? That is up to Allah