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