The Ruling on Vowing Obedience

Question:
If the vow is made to draw near through obedience?

Answer:
If one vows to perform an act of obedience, he must fulfill it. The Prophet (peace and blessings be upon him) said: Al-Bukhari narrated it in his Sahih. So if he says, “I vow to Allah that I will give one hundred riyals in charity to so-and-so,” or “one thousand riyals to so-and-so,” and he is able to do so, he must fulfill it. Or if he says, “I vow to Allah that I will fast on Thursday,” or “fast on Monday,” or “pray two rak'ahs of the Dhuha prayer,” he must fulfill it.

Question: What if he grows old and is unable to fast for two years?

Answer: If he is unable to fast... for two years, fasting for a lifetime is disliked. The Prophet (peace and blessings be upon him) said: “No, the one who fasts forever does not fast.” When Abdullah ibn Amr wanted to fast the entire year, he forbade him, saying: And he said, “I am able to do better than that.” He said: And he forbade him from fasting the entire year. So fasting the entire year is disliked; it is not recommended. Even if he vowed it, he expiates with the expiation for an oath, and that is sufficient.