This is acted upon according to the people of knowledge regarding the permission for the food of the People of the Book.
In-book : Book 21, Hadith 26
English translation : Vol. 3, Book 19, Hadith 1565
21. The Book on Military Expeditions
باب مَا جَاءَ أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ إِذَا أَرَادَ الْحَاجَةَ أَبْعَدَ فِي الْمَذْهَبِ