ANSWER:

This is not true. It is not prohibited to make such a vow but it is not recommended as you oblige yourself to do something Allah didn’t oblige you to do it. Continue your seven days. 

My Grandfather was very sick , he was in critical condition so in that moment I just thought (kind of made commitment) that Allah please gave him health, then I’ll keep 10 fasts. But now I came to know it’s prohibited , I’ve already kept 3 fasts as Alhamdullilah he is fine now so my question is should I keep the rest 7 of them and then refrain from doing such thing. Or I shouldn’t keep them ?

Oaths | December 4, 2018 6:36 am
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When choosing to expiation of breaking an oath; If feeding 10 people, does it have to be cooked? i.e. donating food aid online carity to the poor if clothing, cant it be given online donation? Does it have to be in one go? or separate? i.e feed 2 person each month in the next 5 months is this possible?
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Can a muslim vow and say oh Allah if u do my job I shall fast for so many days. If we had already vowed and Allah bless us , should we keep that fast? Pls guide , may Allah help u in all ur works.