Musannaf Ibn Abi Shaybah

Hazrat Ata, regarding the person who enters the mosque and finds the people in the state of bowing (ruku'), says that when he has passed by the women, he should say Allahu Akbar and perform ruku', then while walking, join the row, and if he catches up with the prostration (sajdah) before that, then wherever he finds the prostration, he should perform it there.