Allah commands justice, the doing of good, and liberality to kith and kin, and He forbids all shameful deeds, and injustice and rebellion: He instructs you, that ye may receive admonition.
Fulfil the Covenant of Allah when ye have entered into it, and break not your oaths after ye have confirmed them: Indeed ye have made Allah your surety; for Allah knoweth all that ye do.[Qur'an 16:90-91]

Narrated Abu Huraira(RA): The Prophet(PBUH) said, "Allah said, 'I will be an opponent to three types of people on the Day of Resurrection: 1. One who makes a covenant in My Name, but proves treacherous; 2. One who sells a free person and eats his price; and 3. One who employs a laborer and takes full work from him but does not pay him for his lab our.' "