بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1042
Marriage
وَلَهُ مِنْ حَدِيثِ جَابِرٍ نَحْوُهُ . وَقَالَ : { فَإِنْ شَاءَ طَعِمَ وَإِنْ شَاءَ تَرَكَ } [1] .
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)."
Sunnah.com reference: Book 8, Hadith 91