Musnad Ahmad 938:49

Waki' narrated to us, Abdullah bin Sa'id bin Abi Hind narrated to us, from Salim Abu an-Nadr, from Busr bin Sa'id, from Zayd bin Thabit, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A person's best prayer is in his house, except for the prescribed (obligatory) prayer."