Surah No. 5, Al Maaeda, part of Ayat No. 1
O you who believe! Fulfill (your) obligations.
Surah No. 17, Al Isra (Bani Israil), Part of Ayat No. 33
The messagae of Allah is very clear, means that all promises made by us must be fulfilled honestly and there should be no deviation from them.
Promises made like providing physical or financial help to the poor must be fulfilled by all means on time. Secondly, if we promise the others regarding paying a visit to them or promise to call back them after some time telephonically then it becomes mandatory on our part to fulfill the covenant.
These are few examples but every promise made by us must be taken seriously and not casually. As a matter of fact we must remember the above decree of Allah and we must act honestly.
Please remember that acting on the above decree of Allah invites rewards but denying the above decree of Allah will have bad effect on our life and will also invite punishment from the Almighty.