Musannaf Ibn Abi Shayba 3:4038

Ibn Idris narrated to us, from Mutarrif, from Abu Ishaq, from Harithah ibn Mudarrib, that Ibn Mas’ud and Abu Musa went out from the presence of Sa’id ibn al-‘As, and the prayer was established. Ibn Mas’ud performed two rak’ahs, then entered into the prayer with the people. As for Abu Musa, he entered into the row.