Question: If someone does some act of kindness for me and I have no other way to repay that person, should I pray to Allah for that person by supplication to Allah on that person's behalf?
If you do a good deed or an act of kindness for another person, you should not expect any reward or recompense from that person whatsoever. You should look forward to your reward from your Lord and from nowhere else.
However, if someone shows you a kindness, you should repay that person in some way if you are able to do so. If you are unable to return the kindness, then you should beseech Allah in supplication for that person. You should do so often, until you feel that you have fully honored the good deed that the person has done for you.
It is authentically related from In `Umar that the Prophet (peace be upon him) said: "Whoever seeks refuge in Allah's name, give him refuge. Whoever begs from you in Allah's name, give to that person. Whoever invites you, accept the invitation. Ad whoever does you a kindness, repay him. If you do not find the wherewithal to repay him, then supplicate to Allah for him until you feel you have compensated him." [Sunan Abî Dâwûd (1672) and Sunan al-Nasâ'î (2567)]
And Allah knows best
Answered by Sheikh Hishâm b. Ismâ`îl al-Sînî, Umm al-Qurâ University