Maliks Muwatta Book 9, Hadith Number 43.

Yahya related to me from Malik that he had heard that Ali ibn Abi Talib said, “Things that pass in front of a man praying do not break his prayer.”

Yahya related to me from Malik from Ibn Shihab from Salim ibn Abdullah that Abdullah ibn Umar used to say, “Things that pass in front of a man praying do not break his prayer.”