from having their contributions accepted from them except that they disbelieved in Allah and in His Messenger, and they do not come to prayer except lazily, nor do they spend except unwillingly.” [al-Tawbah]
If charitable expenditures—whose benefit extends to others—are not accepted from them because of their disbelief, then acts of worship confined to the worshipper himself are even more deserving of not being accepted.
As for the fact that he is not required to make them up when he accepts Islam, the evidence is Allah’s saying: “Say to those who disbelieve: if they desist, they will be forgiven what has already passed.” [al-Anfal: 38] It has also been established through mass transmission from the Messenger of Allah, peace and blessings be upon him, that he did not command those who accepted Islam to make up the obligatory duties they had missed.
But will he be punished in the Hereafter for neglecting them if he does not accept Islam?
The answer is: Yes, he will be punished in the Hereafter for neglecting them, as well as for neglecting all the obligatory duties of the religion. If the Muslim who obeys Allah and adheres to His law may be punished for them, then the one who arrogantly refuses is even more deserving of punishment. And if the disbeliever is punished for enjoying Allah’s blessings of food, drink, and clothing, then committing prohibited acts and neglecting obligatory duties are even more deserving of punishment.
The evidence is what Allah, Exalted is He, mentions concerning the people of the right, who will say to the criminals: “What has brought you into Saqar?” They will say, “We were not among those who prayed, nor did we feed the poor; rather, we used to indulge in vain discourse along with those who indulged in it, and we used to deny the Day of Recompense.” [al-Muddaththir] Thus, they mentioned four reasons, among them the abandonment of obligatory duties.
If someone were to say: “Their denial of the Day of Recompense is disbelief, and that is what brought them into Saqar,”
the response is: They mentioned four reasons, and were it not for these