I made a vow but was unable to fulfill it; is it permissible for me to expiate it with the oath expiation of fasting three days?

The questioner:
May Allah reward you with good, and may He do you good. Honorable Shaykh, this year in Ramadan I broke my fast for six days, and after the month ended, I made them up, praise be to Allah. However, I had intended to fast six days in Shawwal, and I said to myself, “It is obligatory upon me to fast six days in Shawwal as long as I live.” But, Honorable Shaykh, I fell ill and was unable to fulfill my vow, especially since my body is weak. So I decided to fast three days as the expiation for an oath. Is this permissible, Honorable Shaykh? May Allah reward you with good.

The Shaykh:
On the surface of her statement, she said it in her heart and did not make a formal vow, so there is no vow upon her?

The questioner:
What Allah willed.

The Shaykh:
Mere intention or a thought in one’s heart does not bind a person to anything. What binds a person to a vow is only when he verbalizes it and says, “It is obligatory upon me to pray.”