What is better entering salah while the Imaam is in prostration or wait until he raises? -Shaykh ibn al-’Uthaymeen
Question: Is it permissible to make takbeer and enter salah when the Imaam is in sujood (prostration), or should he wait until the Imaam rises into qiyaam (standing)?
Shaykh Muhammad bin Saalih al-’Uthaymeen said: “The best thing to do is to enter the prayer in whatever position the Imaam is in. So if someone comes and the Imaam is in prostration then make the Takbeer and go into sajdah. This is from the statement of the Prophet (peace be upon him),
“…The part of the prayer you get (along with the imam) offer it, and the part you miss complete it (afterwards)…” [Abu Dawud and narrated by Abu Hurayrah]
The reason being that perhaps this prostration that is caught will be a reason for sins being forgiven. Therefore, do not miss out on it. He should make prostration then stand with the Imaam. However, it is not counted as a rak’ah (unit), because the rak’ah is counted if you caught the rukoo’ (bowing).”
By Shaykh Muhammad bin Saalih al-’Uthaymeen may Allah have mercy on him. “Liqaa’atul Baabil Maftooh” 1/408.