Nafi' (may Allah have mercy on him) narrates from Ibn Umar (may Allah be pleased with them both) that Salim (may Allah be pleased with him), the freed slave of Abu Hudhayfah (may Allah be pleased with him), used to lead the first Muhajirun and the Companions (may Allah be pleased with them) from the Ansar in prayer in the Mosque of Quba. Among them were Abu Bakr, Umar, Abu Salamah, Zayd bin Harithah and Amir bin Rabi'ah (may Allah be pleased with them).
The Shaykh says: Perhaps Abu Bakr and Umar (may Allah be pleased with them both) were present at another time, because Abu Bakr (may Allah be pleased with him) came with the Prophet (peace and blessings be upon him); or his leading them in prayer continued before and after the Hijrah, and the narrator meant the time after the Hijrah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5124