It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Whoever asks you by Allah, give to him; whoever seeks refuge with Allah, grant him refuge; whoever does you a kindness, repay him; and if you find nothing (with which to repay him), then pray for him (so much) that you are sure you have repaid him; and whoever asks you for protection in the name of Allah, grant him protection." The chain of this hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it, because there is a disagreement among the students of Imam al-A'mash in narrating it.