Musannaf Ibn Abi Shayba 3:253

Abbad ibn al-Awwam narrated to us, from Abd al-Malik, from Ata, regarding the one who enters the mosque while the Imam is bowing. He said: "When he passes the women, he should say the takbir and bow, then proceed until he enters the row. If the prostration reaches him before that, he should prostrate wherever he reaches."