Allah's Apostle said, "May Allah's mercy be on him who is lenient in his buying, selling, and in demanding back his money."
Sahih Bukhari: Volume 3, Book 34, Number 290
A man asked the Prophet , "What sort of deeds or (what qualities of) Islam are good?" The Prophet replied, 'To feed (the poor) and greet those whom you know and those whom you do not Know
Sahih Bukhari: Volume 1, Book 2, Number 11