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
The Prophet said, "A Muslim is the one who avoids harming Muslims with his tongue and hands. And a Muhajir (emigrant) is the one who gives up (abandons) all what Allah has forbidden."
Volume 1, Book 2, Number 9