Dought & clear - Which is better, to join the imam whilst he is prostrating or to wait until he gets up?.

Is it permissible for the worshipper who missed a rak'ah and found the
imam prostrating to say takbeer and then prostrate, or should he wait
until the imam gets up?.
Praise be to Allaah.
If a person comes and finds the imam in a particular posture he should
join the imam in whatever posture he is in. So if he comes and finds
him prostrating, he should say takbeer and then prostrate, because the
Prophet(peace and blessings of Allaah be upon him) said: "Whatever you
catch up with, pray, and whatever you missed, make it up." And because
the prostration that he does may be a cause of forgiveness of his
sins, so he should not miss out on that. Hence he should prostrate and
then stand up with his imam, but that is not counted as a rak'ah for
him, because the rak'ah can only be caught up with if one catches up
with the bowing (rukoo'). End quote.
Shaykh Ibn 'Uthaymeen (may Allaah have mercy on him).
Liqaa'aat al-Baab il-Maftooh (1/408).