It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Muhajirun said to the Prophet (peace and blessings be upon him): The Ansar have taken away all the reward. He (peace and blessings be upon him) said: "No, as long as you keep praying to Allah for them and praising them." This hadith is sahih (authentic) on the condition of Muslim, and the two Shaykhs (Bukhari and Muslim) did not record it.