Bulugh al-Maram
Book 8, Hadith 91
Arabic hadith text
وَلَهُ مِنْ حَدِيثِ جَابِرٍ نَحْوُهُ . وَقَالَ : { فَإِنْ شَاءَ طَعِمَ وَإِنْ شَاءَ تَرَكَ } 1 .1 - صحيح . رواه مسلم (1430).
Translation
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)."