Maliks Muwatta Book 9, Hadith Number 38.
Section : Warning against Passing in Front of Someone Praying.
Yahya related to me from Malik from Zayd ibn Aslam from Ata ibn Yasar that Kab al-Ahbar said, “If the person who passed in front of a man praying knew what he was bringing on himself, it would be better for him to sink into the ground than to pass in front of him.”