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
Allah's Apostle said, "Whenever you hear the Adhan, say what the Mu'adhdhin is saying.
Sahih Bukhari: Volume 1, Book 11, Number 585