Hadith 318
Sayyiduna Abu Bakrah (may Allah be pleased with him) narrates that he performed rukū‘ before joining the row. The Noble Prophet (peace and blessings of Allah be upon him) said: May Allah increase your eagerness, but do not do this again.
Hadith 319
Sayyiduna Wabisa (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him) saw a man praying alone behind the people (during the congregation), so he ordered him to repeat the prayer.