I say, and with God's success: Fasting is a condition for the validity of obligatory I'tikaf only; as for voluntary I'tikaf, it is not. Aisha (may Allah be pleased with her) said: “The Sunnah for the one in I'tikaf is that he does not visit the sick, nor attend a funeral, nor touch a woman, nor engage with her, nor leave for a need except for what is absolutely necessary, and there is no I'tikaf except with fasting, and there is no I'tikaf except in a congregational mosque.” This is found in Sunan Abu Dawood 2: 333, and Sunan Al-Bayhaqi Al-Kabir 4: 321, and Musannaf Abdul Razzaq 3: 168, and such a narration is only known by hearing, and it has not been narrated that he (peace be upon him) performed I'tikaf without fasting; if it were permissible, he would have done so to teach its permissibility. Aisha (may Allah be pleased with her) also said: The Prophet (peace be upon him) said: “There is no I'tikaf except with fasting” in Al-Mustadrak 1: 606. Al-Tahanawi said in I'laa Al-Sunan 9: 177: Its chain is authentic according to the principle mentioned by Al-Suyuti in the sermon of Kanz Al-'Umal, and Al-Suyuti authenticated it in Al-Jami' Al-Saghir. Al-Qasim ibn Muhammad and Nafi' the freedman of Ibn Umar (may Allah be pleased with them) said: “There is no I'tikaf except with fasting. Allah, the Exalted, says in His Book: {And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the sunset. And do not have relations with them while you are in I'tikaf in the mosques.} Al-Baqarah: 187, for Allah mentioned I'tikaf along with fasting.” And if he vowed to perform I'tikaf while fasting, he is obliged to perform I'tikaf while fasting; if it were not a condition, he would not be obliged, just as if he vowed to perform I'tikaf while giving charity of ten dirhams; this is because a vow is only valid if it is of its kind, obligatory and intended; for it is not for the servant to establish causes or legislate rulings, but rather to impose upon himself what Allah has imposed. And Allah has not made it obligatory to stay alone except within the context of worship, like sitting in the Tashahhud. And because fasting is to abstain from eating, drinking, and sexual relations, then one of the pillars of fasting, which is abstaining from sexual relations, is a condition for the validity of I'tikaf, so likewise the other pillar, which is abstaining from eating and drinking, is equally a pillar of fasting. Therefore, if one of the two pillars is a condition, the other is likewise. Refer to: Al-Tabeen 1: 348, Bada'i Al-Sana'i 2: 109, and Al-Mabsut 3: 116, and Allah knows best.