“Whoever performs Hajj for the sake of Allah, refrains from lewdness and sin, returns as he was on the day his mother gave birth to him.”

Narrated by al-Bukhārī (No. 1819 — the wording is his) and Muslim (No. 1350), from the ḥadīth of Abū Hurayrah, may Allah be pleased with him.

Brief Explanation of the Hadith

Pilgrimage is a great pillar of Islam and a manifest symbol of the religion. It has conditions, essential pillars, and etiquettes that must be observed, as well as prohibitions that must be avoided, so that the pilgrimage may be accepted and the reward abundant.
His statement, “Whoever performs pilgrimage for the sake of Allah,” means sincerely for Him alone, not seeking through it showing off, reputation, or any worldly gain. “And does not engage in sexual relations” — the word refers primarily to marital intercourse, and it is also used for speaking about it explicitly or indirectly, as well as for obscene or indecent speech. And his statement, “and does not commit sin,” refers to disobedience — that is, departing from obedience to Allah by committing acts of sin, whether minor or major. Included in this are insulting others, reviling, cheating, stealing, and all forms of unlawful speech.
Whoever fulfills this, then “he returns like the day his mother gave birth to him,” meaning he returns free from sins, resembling his state on the day he was born — innocent of wrongdoing. This is when he performs the pilgrimage while completing its required conditions and observing its proper manner, such that his pilgrimage becomes an expiation for his sins. The explicit mention of refraining from sin during pilgrimage — even though sin is forbidden at all times — serves to emphasize how especially grave it is in this great and sacred setting. It also highlights the fact that when large numbers of people gather in one place, there is greater likelihood of falling into wrongdoing, particularly in matters related to desire and indecent speech. For this reason, it was specifically and clearly mentioned.
In the ḥadīth there is evidence of the great virtue and importance of pilgrimage, and of the obligation to purify one’s intention in performing it. It also shows that a pilgrimage fulfilled with its proper conditions expiates sins — both minor and major. However, as for the rights of other people, their rights must be restored to them along with sincere repentance.