Can Hajj atone for the sins of those who did not perform it, especially the sin of abandoning prayer, whether they enjoined it or not, and can it atone for the sins of those who perform Hajj for themselves, especially the sin of abandoning prayer?

Abandoning prayer is a grave sin. Scholars have differed on the issue of whether one who abandons prayer is an unbeliever. The correct view is that he is an unbeliever (kafir), an apostate from Islam, based on the Prophet's (peace be upon him) saying: "The covenant between us and them is prayer; whoever abandons it has disbelieved," and his saying: "Indeed, between a man and polytheism and disbelief is the abandonment of prayer."

The Companions unanimously agreed on the disbelief of one who abandons prayer, and many scholars after them also held this view. Prayer is the first thing a servant will be questioned about on the Day of Judgment, and abandoning it nullifies deeds. Allah the Almighty says: "And We shall turn to whatever deeds they did and make them as scattered dust." And the Prophet (peace be upon him) said: "Whoever abandons the Asr prayer, his deeds are nullified."

If one who abandons prayer performs Hajj while persistent in abandoning it, his Hajj is not valid. And if one dies while persistent in abandoning prayer, it is not permissible to supplicate for his forgiveness or perform Hajj on his behalf, because he is an unbeliever. However, if one who abandons prayer repents and returns to Islam, Allah forgives all his past sins. Allah the Almighty says: "Say to those who have disbelieved, if they cease, what has passed will be forgiven them." And the Prophet (peace be upon him) said: "Islam demolishes what came before it."