Sunnah.com reference : Book 8, Hadith 91English translation : Book 8, Hadith 1053Arabic reference : Book 8, Hadith 1042
Muslim has something similar to the above from the Hadith of Jabir (RA), it goes:
"If he wishes he may eat, and if he wishes he may leave (the food alone)."
وَلَهُ مِنْ حَدِيثِ جَابِرٍ نَحْوُهُ .‏ وَقَالَ : { فَإِنْ شَاءَ طَعِمَ وَإِنْ شَاءَ تَرَكَ }   1‏ .‏‏1 ‏- صحيح .‏ رواه مسلم (1430)‏.‏