Validity of corrections made before the Imam rises from Ruku'

Primary text

If a follower makes *takbir* alone behind the Imam, then advances to the Imam's right, or another person joins him, or he advances to stand in a row in front of him, or if two people start, one hesitates and then makes *takbir* before the Imam rises from Ruku', or if one person is on the right and senses another joining, and he moves back before the second makes *takbir*, or if he makes *takbir* to the left, his prayer is valid. This is distinguished from praying a complete *rak'ah* alone behind the row.