Prophet Muhammad (saw) said, "There are three persons whom Allah will not look at on the Day of Resurrection, nor will he purify them and theirs shall be a severe punishment. They are: 1. A man possessed superfluous water, on a way and he withheld it from travelers. 2. A man who gave a pledge of allegiance to a ruler and he gave it only for worldly benefits. If the ruler gives him something he gets satisfied, and if the ruler withholds something from him, he gets dissatisfied. 3. A man displayed his goods for sale after the 'Asr prayer and he said, 'By Allah, except Whom None has the right to be worshipped, I have been given so much for my goods,' and somebody believes him (and buys them)." The Prophet then recited: "Verily! Those who purchase a little gain at the cost of Allah's Covenant and their oaths." (3.77)

Sahih Al-Bukhari Vol. 3 : No. 547

Prophet Muhammad (saw) said, "Procrastination (delay) in repaying debts by a wealthy person is injustice."

Sahih Al-Bukhari Vol. 3 : No. 585