He who vowed to obey Allah, should obey Him
'Aishah (May Allah be pleased with her) said:
The Prophet (may the peace and blessings of Allah be upon him) said, "He who vowed to obey Allah, should obey Him. But he who vowed to disobey Allah, should not disobey Him."
[Al- Bukhari].
Vowing is one of the permitted things, provided that it implies drawing closer to Allah.
In some cases vowing would be recommended, as in the case of expressing thanks for Allah because of a blessing.
In some cases vowing would be disliked, if it is contingent on something that one wants from his Lord – the Almighty - as if to say: If Allah healed me I will slaughter a ram, or I will pray one hundred rak'ahs, or I will fast two days a week; This vow is not befitting to Allah. Because one seeks through his vow to obtain a thing that is not decreed for him, or to ward off anything that Allah has decreed for him.
From this statement we understand that the saying of the Prophet (may the peace and blessings of Allah be upon him) said, "He who vowed to obey Allah" refers to performing the recommended matters, or to perform the obligatory matters with certain conditions identified by the one who vows, with the intention of seeking closeness to Allah, to discipline the disobedient soul and to restrain the self inclination.
Let the one who vowed to do a recommended mater do his best to fulfill it. It is like a dept that must be settled unless he is unable to fulfill it.
One may not slacken to fulfill his vow, for if he fails to fulfill his vow, he will not be one of the righteous whom Allah has promised the abundant reward.
The saying of the Prophet (may the peace and blessings of Allah be upon him) " But he who vowed to disobey Allah, should not disobey Him." Means that it is expressly forbidden to fulfill it, because fulfilling it is contrary to fulfilling the right of Allah, so that it is not considered an act of worship, but rather a sin. It also includes a prohibition of the vow of sin.
One should not overburden himself with the matters that he does not have the ability to do, or with what brings hardship, or diseases and illnesses which he can not endure. The vow is intended to seeking closeness to Allah but one can not draw closer to Allah with the prohibited things or with what is beyond the legally recommended matters.
It is taken from this Hadeeth above what is said: that in principle: the vow of sin is not permissible, even if one uttered it, it will not count and it must not be fulfilled, the one who utters it is considered to be a sinner in any case.
Allah is the Most Merciful. The entirely Merciful and the one who likes to pardon and forgive.
everyone is well aware of himself, it is wise not to overburden oneself with what is hard on him, but one shall adopt an easy approach to fulfill the obligatory and the recommended matters as much as he can.