Musannaf Ibn Abi Shayba 3:2243

Hushaym narrated to us, he said: Husayn informed us, from Hilal ibn Yasaf, from Abu Hayyan al-Ashja‘i—and he was among the companions of ‘Abdullah—he said: Do not hasten before your Imams in bowing (ruku‘) nor in prostration (sujud). And if one of you raises his head while the Imam is prostrating, then let him prostrate, then let him remain for the duration of what the Imam preceded him by.