Whoever enters the Mosque while the Imam is bowing

Question :

If I came to congregation prayer in the mosque while they are praying and are bowing, should I join with them by making the opening Takbir and the Takbir for bowing, and should I recite the opening supplication or not?

Answer:

When a Muslim enters the mosque and the Imam is bowing, it is prescribed for him to join with him, pronouncing two Takbirs the opening Takbir while he is standing, then the second Takbir for the bowing as he bends down for it, but it is not lawful at this time to recite the opening supplication, nor Surah Al-Fatihah due to the shortness of time.

This Rak'ah is credited to him, according to the authentic Hadith narrated by Al-Bukhari, on the authority of Abu Bakrah Ath-Thaqafi, may Allah be pleased with him, who reported that he entered the mosque one day, and he found the Prophet in bowing and so he bowed behind the row, then he entered the row. And the Prophet said to him:
"May Allah increase you in endeavor, but do not repeat it."

He did not order him to make up for it, which proves that it was sufficient for him. And that it is incumbent upon one who enters and finds the people bowing to join the row and not to bow behind the row, even if he should miss the Rak'ah. This is because the Prophet said to Abu Bakrah:
"May Allah increase you in endeavor, but do not repeat it." And Allah is the Granter of success.

Source:
Ibn Baz
Fatawa Islamiyah, Vol. 2 Pages 138-139