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 faithful believer to a faithful believer is like the bricks of a wall, enforcing each other." While (saying that) the Prophet clasped his hands, by interlacing his fingers.
Sahih Bukhari: Volume 1, Book 8, Number 468