Musnad Abu Ya'la al-Mawsili 105:42

Musa narrated to us, Wahb bin Jarir narrated to us, my father narrated to us, he said: I heard Qays bin Sa'd narrating from 'Ata', from Muhammad bin 'Ali bin Abi Talib, from 'Ammar bin Yasir, that he greeted the Prophet, peace and blessings of Allah be upon him, while he was praying, and he returned the greeting to him.