(a) Al-Hasan (may Allah have mercy on him) narrates from Sayyiduna Abu Bakrah (may Allah be pleased with him) that when he came, the people were in bowing, so he bowed before reaching the row and then walked towards the row. When the Prophet (peace and blessings be upon him) had completed his prayer, he said: "Who bowed before reaching the row and then joined the row?" Sayyiduna Abu Bakrah (may Allah be pleased with him) said: O Messenger of Allah! It was me. He (peace and blessings be upon him) said: "May Allah increase your eagerness; do not do this again."
(b) In the hadith of al-Rudhbari it is that when Sayyiduna Abu Bakrah (may Allah be pleased with him) came, the Messenger of Allah (peace and blessings be upon him) was in the state of bowing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5215