I want to know that one person says to Allah (he makes niyat) that if I do that sin I will make 1000 fast, but now he is unable to do this, as he is human being 1000 fast is like a big mountain. He tried but now he is upset. He is not able to do this. So he wants to ask whether he can give any kaffarah or sadaqah for the 1000 fasts.
بسم الله الرحمن الرحيم
(Fatwa: 940/735/H=9/1434)
If someone intended that if he commits sin he will keep hundred fasts, and then he committed the same sin, so though these fasts are not wajib (compulsory) on him, but it is better for him to keep the fasts one by one. However, if one is unable to do so, then it is better that he pays wheat equal to Sadaqah al-Fitr (1.633 kg) or its price for one fast to the poor and needy ones. Also, you should keep on doing true taubah from the sin you committed. If it is hard to fast in summer days, you may keep them in winter; however it will also suffice if you give fidyah (expiation).
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband