Umar bin al-Khattab (may Allah be pleased with him) narrates: At al-Ji'ranah I said: O Messenger of Allah! I owe a day of i'tikaf. The Prophet (peace and blessings be upon him) said: "Go, perform the i'tikaf, and fast as well."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8576
Ali bin Umar al-Hafiz (may Allah have mercy on him) states that Ibn Budayl alone narrates it from Amr, and he is da'if (weak) in hadith.
Ali said: I heard Abu Bakr al-Naysaburi say: This hadith is munkar (rejected), because the reliable students of Amr bin Dinar did not mention it, among them Ibn Jurayj, Ibn Uyaynah, Hammad bin Salamah, Hammad bin Zayd and others; and Ibn Budayl is weak in hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8577
Abdullah bin Umar (may Allah be pleased with them both) narrates from Umar bin al-Khattab (may Allah be pleased with him) that during the time of polytheism he had vowed to perform i'tikaf and to fast. After accepting Islam he asked the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) ordered him to fulfil the vow.
(The mention of the vow of fasting together with i'tikaf comes through a gharib (unusual) chain.)
Sa'id bin Bashir alone narrated it from Ubaydullah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8578
Sayyidah Aishah (may Allah be pleased with her) narrates that she said: "There is no i'tikaf without fasting."
(Al-Zuhri narrated a hadith from Urwah from Sayyidah Aishah (may Allah be pleased with her), at the end of which it says that the sunnah for one who performs i'tikaf is that he fasts.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8579
Urwah narrates from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: "There is no i'tikaf except with fasting."
(Ata narrates from Sayyidah Aishah (may Allah be pleased with her) as a mawquf report: Whoever performs i'tikaf must fast.)
This is an error (wahm) on the part of Sufyan bin Husayn or Suwayd bin Abd al-Aziz; Suwayd bin Abd al-Aziz al-Dimashqi is very weak, and what he alone narrates is not accepted.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8580
Amr bin Dinar (may Allah have mercy on him) narrates from Abu Fakhitah, who said: I heard Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) saying: Only one who is fasting may stay (in i'tikaf).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8582
Sa'id bin Ilaqah narrates: I heard Abdullah bin Abbas (may Allah be pleased with them both) saying: The mujawir should fast; and mujawir means the mu'takif (one in i'tikaf).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8583
Amr bin Dinar (may Allah have mercy on him) narrates that a man asked: O Abu Muhammad! What about the saying of Ibn Abbas (may Allah be pleased with them both): "Fasting is upon the mujawir (one in i'tikaf)"? Amr (may Allah have mercy on him) said: Ibn Abbas (may Allah be pleased with them both) did not say it like that; he only said: "The mujawir fasts."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8584
Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) and Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) both said that it is necessary for the mu'takif (the one performing i'tikaf) to be fasting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8585