Someone made a vow to fast then did something deliberately that broke his fasting. Please comment.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Whoever vows to fast a day must fast that day. Now, if he started the fasting and then did anything that nullifies it, then he should make that day up.

For more benefit on fulfilling a vow and whether or not it requires repetition, please refer to Fataawa 8800, 1125, 29377, 367117, 119549, 138168 and 249157.

Also, for more benefit on the expiation for breaking a vow, please refer to Fatwa 102811.

Allah knows best.