Answered by Shaykh Amjad Rasheed
How can I reverse an oath that I made by saying, “By Allah, I will perform tahajjud for my entire life.”
This is a valid oath and an oath to do good, so it is better not to break. Rather, the one who made the oath should persist in it. If he misses a night and doesn’t perform tahajjud during it, he has thereby broken his oath, but he isn’t sinful. However, he does have to expiate for a broken oath, which is to:
1. Free a slave (which can’t be done today); or to
2. Feed ten needy people, giving each a mudd ([m: approximately 0.51 litres]) of wheat, rice, or the like. (The Hanafi masters permit giving the value of the food in money.); or to
3. Clothe [m: ten needy people].
One is free to choose any one of the above to act upon. If one can’t perform any of them, then one fasts three days, whether continuously or separately.