One Who Vows to Stand in Prayer All Night and Is Unable to Do So

Question:
If a person vows to stand in prayer until morning, but he is unable to do so, what is required of him in the situation described?

Answer:
This is a continuation of the answer regarding cauterization. The questioner says that the Messenger (peace and blessings be upon him) forbade torturing with fire, and that no one should be tortured with fire except the Lord of the Fire. However, cauterization was excepted for the sake of necessity and the benefit it provides. The question he asked is that he vowed to pray all night. This is not a vow to worship all night.
So he should pray as much of the night as is easy for him and sleep the rest of the night. He should not pray all night and stay awake all night, because Allah has not commanded that. The Prophet (peace and blessings be upon him) said, “I pray and I sleep.” When it was reported to him about the man who said, “As for me, I pray and I do not sleep,” he said, “As for me, I pray and I sleep.” So he should pray, for example, one-third of the night or half the night, and that is sufficient, if Allah wills.