Praise be to Allaah.
If a person is deemed to be a kaafir, all his deeds are
invalidated. Allaah says (interpretation of the meaning):
“But if they had joined in worship others with Allaah, all
that they used to do would have been of no benefit to them”
disbelieves in Faith, [i.e. in the Oneness of Allaah and in all the other
Articles of Faith i.e. His (Allaah’s) Angels, His Holy Books, His
Messengers, the Day of Resurrection and Al‑Qadar (Divine Preordainments)],
then fruitless is his work; and in the Hereafter he will be among the losers”
A number of scholars are of the view that he is a not a
kaafir in the sense of major kufr if he affirms that prayer is obligatory,
but he is guilty of minor kufr, and this action of his is worse and more
abhorrent than the action of the adulterer or thief and the like. Despite
that, his fasting and Hajj are still valid, in their view, if he does them
in the proper manner as prescribed in Islam. But his offence is that he is
not praying regularly, and he is in grave danger of falling into major shirk
according to a number of scholars. Some of them narrated that the majority
are of the view that he is not a kaafir in the sense of major kufr if he
does not pray because he is lazy or heedless, rather he is committing minor
kufr thereby, but his crime is still serious and an abhorrent evil that is
worse than adultery, stealing, disobeying one’s parents, drinking alcohol
and so on. We ask Allaah to keep us safe and sound.
But the more correct of the two scholarly views is that he is
a kaafir in the sense of major kufr – we ask Allaah to keep us safe and
sound – because of the shar’i evidence quoted above. So if a person fasts
but does not pray, his fasting does not count, and neither does his Hajj.
Majmoo’ Fataawa al-Shaykh Ibn Baaz (15/179).