The Messenger of Allah ﷺ said, "Whoever seeks refuge in the name of Allah, grant him refuge. Whoever asks in the name of Allah, give to him. Whoever invites you, accept his invitation. Whoever does you a favor, repay him. If you cannot find the means to repay him, then pray for him until you feel that you have indeed repaid him."
قال رسول الله ﷺ: من استعاذ بالله فأعيذوه، ومن سأل بالله فأعطوه، ومن دعاكم فأجيبوه، ومن صنع إليكم معروفا فكافئوه، فإن لم تجدوا ما تكافئونه، فادعوا له حتى تروا أنكم قد كافأتموه.
Narrated by Abu Dawud (1672, 5109), Nasai (2568), and Ahmad (5365), and Ibn Hibban (3408) and Hakim (2/63-64) both graded it sahih, all of them via Amash, from Mujahid, from Abdullah bin Umar, who related it. Its chain of transmission is sahih. Hakim said, "Sahih in its chain of transmission according to the standard of the two Shaykhs, though they did not include it due to disagreement among the companions of Amash." A detailed discussion of this is found in the chapter on zakat.