338 – Abu Bakrah (may Allah be pleased with him) reported: “He reached the Prophet ﷺ while the Prophet was already in bowing posture, so he himself bowed before he reached the row. He later mentioned this to the Prophet ﷺ, who said to him, ‘May Allah increase your eagerness, but do not do that again.’ ” Recorded by al-Bukhari.
Abu Dawud adds: “He bowed behind the row and then walked forward to the row.” (1)

Glossary of the ḥadith
– ḥirṣan: pronounced with a kasrah on the ḥāʾ, a sukun on the rāʾ, and a fatḥah on the ṣād; it means a strong desire for good and hastening toward it.
– wa-lā taʿdu: the sounder of the three transmitted forms is “wa-lā taʿdu,” with a fatḥah on the tāʾ, a sukun on the ʿayn, and a ḍammah on the dāl. Its final letter is a wāw (the third radical) that is omitted because the verb is jussive after the prohibitive particle lā. It comes from al-ʿadw, which is rapid running, the opposite of calm and dignity. Another reading has “taʿud,” with a fatḥah on the tāʾ and a ḍammah on the ʿayn, meaning: do not hasten in order to catch the rakʿah by bowing outside the row.

Points derived from the ḥadith
1 – Whoever reaches the imam while the imam is bowing and bows behind the row before joining it—or stands beside someone at the end of the row—his bowing is valid and he has caught that rakʿah.
2 – A small amount of movement in prayer, when it serves the prayer itself, does not harm or invalidate the prayer.
3 – A rakʿah is deemed attained by catching the bowing with the imam. The Prophet ﷺ accepted his rakʿah; had it not counted, he would have ordered him to repeat it, just as he commanded the man who prayed incorrectly to repeat his prayer. A person is excused for shortcomings in an act of worship whose time has already passed when those shortcomings occurred out of ignorance