Whenever you enter the masjid, you must join the Imam regardless of the position he is in.
If you manage to perform ruku while he is in ruku, this Rakah is valid.

In fard prayer when I find the imam in rukuh I don’t join him there rather wait for him to go to sujood and then I join him. Because I know that without fatiha my rakah is invalid. But I have also heard you saying if I join during rukooh my rakah is valid. Which one is corrert?

Prayer |