And if he has intercourse in the vagina, his i‘tikaf is invalidated.
His statement, “And if he has intercourse in the vagina,” refers to the person observing i‘tikaf.
His statement, “his i‘tikaf is invalidated,” means that it becomes null. Invalidity and nullity are synonymous except in two cases. The first concerns Hajj and ‘Umrah: an invalid Hajj or ‘Umrah is one invalidated by intercourse, whereas a null one is one nullified by apostasy from Islam. The second concerns marriage: a null marriage is one whose nullity is unanimously agreed upon by the scholars, such as marrying a woman who is observing her waiting period; whereas an invalid marriage is one concerning which they differ, such as a marriage conducted without witnesses.
The evidence that intercourse invalidates i‘tikaf is the saying of Allah, Most High: “And do not have relations with them while you are observing i‘tikaf in the mosques.” [2:187] This indicates that relations with women are not permitted during i‘tikaf. Therefore, if he has intercourse, his i‘tikaf is invalidated, because he has done something specifically prohibited. Everything specifically prohibited within an act of worship invalidates it. Here, there are certain principles:
First: if the prohibition pertains to the act of worship itself, then it is forbidden and invalid.
An example is if a person fasts on the day of Eid: his fast is forbidden and invalid, because the Prophet, peace and blessings be upon him, prohibited fasting on the day of Eid. Likewise, if a woman fasts while menstruating, her fast is forbidden and invalid, because she has been prohibited from doing so. The Prophet, peace and blessings be upon him, said: “Whoever performs an action that is not in accordance with our command, it is rejected.” That is, it is rejected. Whatever has been prohibited is not in accordance with the command of Allah and His Messenger. Moreover, if we were to deem an act of worship valid despite its prohibition, this would constitute a form of opposition to the command of Allah, Most High.
Second: if the prohibition pertains to a statement or action specific to the act of worship, this likewise invalidates the worship.
An example of this is that if a person speaks during the prayer—even to enjoin what is right—his prayer is invalidated.