Full Sharh — Riyad as-Salihin 1044
وعن ابن عمر رضي الله عنهما قال: قال رسول الله صلى الله عليه وسلم : "من استعاذ بالله فأعيذوه، ومن سأل بالله، فأعطوه، ومن دعاكم فأجيبوه، ومن صنع إليكم معروفًا فكافئوه، فإن لم تجدوا ما تكافئونه به، فادعوا له حتى تروا أنكم قد كافأتموه". ((حديث صحيح رواه أبو داود والنسائي بأسانيد الصحيحين))
English Translation
Ibn 'Umar (May Allah be pleased with them) said:: The Messenger of Allah (ﷺ) said, "Grant shelter to him who begs for it in the Name of Allah, give to him who begs in the Name of Allah, accept the invitation of him who invites you, and requite him who does a favour to you, but if you are unable to requite him, go on praying for him till you are sure that you have requited him adequately.".
Source
Riyad as-Salihin(رياض الصالحين)
The Book of the Prohibited actions
Hadith Number
1044