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