Maliks Muwatta Book 008, Hadith Number 004.

Section : The Superiority of Prayer in Congregation over Prayer Done Alone.

Yahya related to me from Malik from Abu'n-Nadr, the mawla of Umar ibn Ubaydullah from Yusr ibn Said that Zayd ibn Thabit said, "The most excellent prayer is your prayer in your house, except for the prescribed prayers."