Made a promise to do something, but now wants to cancel it
13-8-2015 | IslamWeb
Question:
I made a serious promise in a state of extreme anger to file a report against the principal of my children's school because he did not accept my request to transfer my child to another class. Later on, unsure of its lawfulness, I changed my mind about filing the report. How can I solve this problem? What should I do (about my vow)? I fear that committing a sin for which I will be held accountable before Allaah, the Exalted.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
You said, "I made a promise to do such and such thing," this could mean that you decisively intended to file a report against that teacher without uttering this by your tongue. It could also mean that you made an oath to file a report against him or made a vow to do so, saying, "If I do not file a report against him, I will fast such-and-such days or offer such-and-such in charity," or whatever.
Based on the first possibility, it is not incumbent on you to do anything in this regard. According to the second possibility, you are obliged to offer expiation for breaking an oath, even if you did not do that act about which you made your oath. When a person makes an oath to do something and then found out that it is better not to do it, he should offer expiation for breaking his oath. As for the third possibility, you have the choice either to deliver on your vow, if you are fair regarding the complaint you are planning to file against this teacher, or to offer expiation like that of breaking an oath. This is because such a vow is known as vow of lajaj (i.e. vow of anger). This is a vow whereby the person urges himself to do something or abstain from doing something but does not intend thereby to do a righteous act that brings him closer to Allaah, the Exalted. Al-Khateeb Ash-Shirbeeni 
said:
"It (the vow of lajaj) resembles a vow in terms of committing oneself to perform an act that brings one closer to Allaah and resembles an oath in terms of urging oneself not to do a certain act. As it is not proper to oblige the person to act upon both of them (vow and oath) or neglect both of them, it is more appropriate to let the person choose whether to fulfill it or not to fulfill it." [Mughni Al-Muhtaj]
This means that, in this case, the vow-maker has the choice either to fulfill his vow or break it and offer an expiation like that for breaking an oath.
Allaah Knows best.