Musannaf Ibn Abi Shaybah

Hazrat Sha'bi narrates that Hazrat Sa'd and Hazrat Ammar performed three rak'ahs of prayer. When they were informed, they completed the remaining prayer and said salam, then said takbeer and performed sajdah, then said takbeer and raised their heads, then said takbeer and performed sajdah, then said takbeer and raised their heads.