Hazrat Anas (radhiyallahu ‘anhu) narrates, “No Ansaari Sahaabi regarded himself as being more deserving of his wealth than his Muhaajir brother.”
Hence, when the Muhaajireen witnessed the unmatched compassion and unrivalled sacrifices of the Ansaar, they said, “O Rasul of Allah! These people whom we have come to and settled among are such that we have not come across anyone more compassionate, more sincere in giving comfort to us, and more devoted than them, as whether in times of comfort or hardship, they are always prepared to assist. We fear that they will acquire all the reward while we will be deprived of reward.” Rasulullah (sallallahu ‘alaihi wasallam) replied, “No, you will not be deprived of reward so long as you continue making dua for them.”
In other words, the kindness one may show someone through making dua for them is no less than the kindness one receives from them in the form of gold and silver. Rather, the kindness of making dua for them is even superior to the kindness of receiving wealth from them. Let alone a few dirhams, if the riches of the entire world were to be placed on one pan of the scale and just a single sincere dua is placed on the other pan, then insha Allah the pan of dua would outweigh the pan of riches (as one is begging Allah Ta‘ala to bestow His special grace upon the person, and the treasures of Allah Ta‘ala are unlimited).
(Extracted from Seeratul Mustafa 1/439-440)