Musannaf Ibn Abi Shaybah 39130 — Sitting twice in the Friday sermon

Ata said: A man prayed the morning prayer with the Prophet (peace and blessings be upon him). When he (peace and blessings be upon him) had finished the prayer, that man stood and prayed two rak'ahs. The Prophet (peace and blessings be upon him) asked him: "What are these two rak'ahs?" He said: "O Messenger of Allah (peace and blessings be upon him)! I came (to the mosque) while you were in the prayer, and I had not prayed the two rak'ahs before Fajr. I disliked praying those two rak'ahs while you were leading the prayer. So when you had completed the prayer, I prayed those two rak'ahs." The narrator says: He (peace and blessings be upon him) neither commanded him nor forbade him (from it).