The Quran says: وَالْمُوفُونَ بِعَهْدِهِمْ إِذَا عَاهَدُوا (2:177) “Believers are those] who keep their pledges when they make them.” There are two sides in any promise. When you pledge your word to another person, that makes a promise. Promise is always bilateral. When you have made a promise, fulfilling it is very essential. Believers are those who fulfil the promises they have made. People make a promise but don’t have the sensitivity to fulfil it. When you remind them, they say they had forgotten and would fulfil it the next day. This is completely impermissible in Islam. If you have made a promise, you have to remember it. When you have made a promise, you must fulfil it and never forget about it. You must write it down on paper. If you can't remember, you should note it down on paper.

I read a book in my childhood which said you should write down and if you forget, you must look back. When you write down something, it gets recorded. Maintaining a diary is also among the Sunnah of the Prophet. You should have something to write down every day. If you have made a promise to someone, write it down as people note down phone numbers. You should note everything in your diary. You must write about your learning this day. You should write about the promise you made to someone. You should also mention the mistakes you made this day. Write what you learnt and what you didn’t learn. Writing a diary is also part of Islam.