I say, and with God's success: I'tikaf is invalidated by the following: First: ejaculation through sexual intercourse and its causes: whether intentional or forgetful, during the day or at night, even outside the mosque; because it is prohibited by text, thus it invalidates it in any case, unlike fasting where it is not invalidated if it is forgetful. The difference is that the state of the person in I'tikaf is one of remembrance: like the state of Ihram and prayer, while the state of fasting is not one of remembrance. However, if one ejaculates by looking or has sexual intercourse without penetration and does not ejaculate, his I'tikaf is not invalidated: just as fasting is not invalidated by it. Second: apostasy from Islam – may Allah protect us – if one apostatizes, the I'tikaf is invalidated by his apostasy, and he does not build upon what has passed, nor does he have to make up for the obligatory I'tikaf if he returns to Islam; as Allah Almighty says: {Say to those who disbelieve, if they cease, what has passed will be forgiven for them}, Al-Anfal: 38, and His Messenger (peace be upon him) said: 'Islam wipes out what was before it' in Musnad Ahmad 4: 198. Third: fainting and insanity if they last for a time that prevents the intention for fasting, and he must make up the I'tikaf during them. Fourth: leaving without a valid excuse, even if forgetfully, and the valid excuses for I'tikaf include: Friday, urination, defecation, and washing if he has a wet dream and cannot wash in the mosque, the collapse of the mosque, being forcibly removed by an oppressor, fearing for himself or his belongings from aggressors. However, illness, visiting the sick, attending a funeral, rescuing a drowning person or a fire victim, going out for jihad, or to bear witness are not valid excuses for leaving I'tikaf, as it invalidates his obligatory I'tikaf if he leaves for them. Refer to: Al-Hadiyyah Al-Ala'iyyah p. 185, Al-Taa'liqat Al-Mardiyyah p. 185, Al-Wiqayah p. 245, Al-Mabsut 3: 123, Al-Tabeen 1: 352, and Allah knows best.