Those who say: If you join the imam in ruku and place your hands on your knees before he rises, you have attained the rak‘ah

Hazrat Ibn Umar (may Allah be pleased with them both) narrates that if you find the Imam in the state of bowing (ruku‘) and before he raises his head you place your hands on your knees, then you have attained that rak‘ah.

Hazrat Saeed bin Al-Musayyib says that whoever joins the imam in bowing (ruku) before the imam raises his head, he has attained that rak'ah.

Hazrat Dawood said that he asked Hazrat Sha'bi about a man who joins the congregation while the people were in ruku', but the Imam had already raised his head; what is the ruling on this? He replied: You are Imams to one another.

Hazrat Maymoon says that when you enter the mosque and see people bowing (ruku‘), say the takbeer and bow before they raise their heads, then you have attained that rak‘ah.