Keeping Promises:
Keeping promises means to fulfill promise keep your words and be firm on that promise. Keeping promise is called fulfilling commitment. It is repeatedly advised in Quran and hadees.
"Fulfilling promise" in light of Quran:
Among mutual relations of human beings, the importance of keeping promise is very well known. The base of our many dealings is on promises. If those are fulfilled, then our dealings are fine and if it is not done so, then it is otherwise. Islam insists on keeping promise to strengthen relations among each other.
Allah says in Quran:
وَأَوْفُوا العَهْدِ إِنَّ الْعَهْدَ كَانَ مَسْئُولًا ) (سارا :34)
Translation: Indeed, the commitment is over (that about which one will be) questioned.
The most important promise among the all is ones that very commitment which human beings were there to make on the day immemorial with their Lord on being His slaves. Quran reminds us about this in the following way.
وَبِعَهْدِ اللهِ أَوْفُوا ذَلِكُمْ وَكُمْ بِهِ لَعَلَّكُمْ تَذكرون (الانعام:152)
Translation: And the covenant of Allah fulfill. This has He instructed you that you may remember.
In another verse, Quran reminded about mutual commitments and collective relations in this manner.
الَّذِينَ يُوفُونَ بِعَهْدِ اللهِ وَلَا يَنقُضُونَ الْمِيثَاقَ : وَالَّذِينَ يَصِلُونَ مَا أَمَرَ اللهُ بِهِ أَنْ يُوصَلَ
(الرعد: 21,20)
Translation: Those who fulfill the covenant of Allah and do not break the contract, and those who join that which Allah has ordered to be joined.
ii. Keeping promise in light of Hadees:
Hazrat Muhammad followed his promises in all type of severe circumstances. For instance, when at time of Hudaibiya pact, Abu Jandal tied in chains came to him and requested him to be taken to Madinah and instead of that affection which he had with Muslims, Holy Prophet refused to take him to Madinah as the pact had been done with Quraish that Muslims escaping from Makkah and going to Madinah would be returned to Makkah.
Hazrat Abu Jandal's miserable condition was the source of dissatisfaction for all companions but all were patients because of following the pact.
Hazrat Anas said that often messenger of Allah used to say in his sermons.
لَا دِينَ لِمَنْ لَّا عَهْدِلَهُ
Translation: A person who doesn't keep his promise, does not have Deen.
iii. Keeping promise and character of Holy Prophet
From seerah (Character) of the Holy Prophet, we get the best model of keeping promises and even his enemies confessed about his quality of fulfilling commitments.
The Incident of Abu Hasma:
Hazrat Abdullah bin Abu Hasma says, "I did a bargain with the Holy Prophet before the prophet hood was bestowed on him. I had to pay him some money. I promised the Holy Prophet that I will bring that money here and when I went home, 1, forgot it, I remembered after three days, what I saw that Rasullulah was present there", Hazrat Muhammad said this only, "You have hurt me a lot I have been waiting here for you for three days". (Abu Dawood).
Incident of Abu Jabal
In the Battle of Bader, the number of Muslims was hugely less than that of non- Muslim army. Every person was needed severely. At this occasion, two companions, Huzaifah bin Al Yaman and Abu Jabal were arrested by disbelievers. They both were freed on this condition that they would not be a part of Muslims in war against them. They came and narrated to the Holy Prophet the whole story. He directed them to fulfill their promise which they made with infidels. Therefore, those both of the companions didn't participate in the battle of Bader.