Musnad Ahmad 25:613

Husayn narrated to us, Abd al-Hamid ibn Bahram narrated to us, from Shahr ibn Hawshab, who said: Abdullah ibn Abbas said: A group of Jews attended the Messenger of Allah, may Allah bless him and grant him peace, and said: "O Abu al-Qasim, tell us about traits we will ask you about, which no one knows except a prophet." Among what they asked him was: "Which food did Israel (Jacob) forbid for himself before the Torah was revealed?" He said: "I adjure you by Allah, who revealed the Torah to Moses, do you know that Israel, Jacob, peace be upon him, fell severely ill and his sickness lasted long, so he made a vow to Allah that if Allah cured him of his sickness, he would forbid for himself the drink most beloved to him and the food most beloved to him? And the most beloved food to him was camel meat, and the most beloved drink to him was its milk." They said: "By Allah, yes."