Isma'il bin Salim narrates from Mujahid (may Allah have mercy on him) that the Prophet (peace and blessings be upon him) ordered the man who had left one day's fast in Ramadan that "his expiation is the expiation of zihar."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8069