حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، قَالَ: حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، أَنَّ الْمُهَاجِرِينَ قَالُوا: يَا رَسُولَ اللهِ، ذَهَبَ الأَنْصَارُ بِالأَجْرِ كُلِّهِ؟ قَالَ: ”لَا، مَا دَعَوْتُمُ اللَّهَ لَهُمْ، وَأَثْنَيْتُمْ عَلَيْهِمْ بِهِ.“
It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Muhajirun said: O Messenger of Allah! The Ansar have taken all the reward. The Prophet (peace and blessings of Allah be upon him) said: "That is not so, as long as you pray for them and mention them with words of praise."
Explanation & Benefits
Shaykh Maulana Usman Muneeb
Benefits and Issues:
From this hadith, it is understood that just as the one who does good (ihsan) and gives gifts, etc., receives reward, similarly, the one who prays in return and praises the benefactor also receives the reward for that supplication and praise. However, this is in the case when a person is truly not in a position to return the favor. If someone has the ability to return the favor but does not do so and merely says "Jazak Allahu khayran," then perhaps he is not deserving of this reward.
Source: Fadlullah al-Ahad: Urdu Commentary on al-Adab al-Mufrad, Page: 217