Yusuf ibn Abdullah ibn Salaam says, I once observed Rasoolullah sallallahu alaihe wasallam take a piece of bread and put a date on it and say, "This (date) is the curry for this (bread)." He then ate it. (FR)
English reference (FR): Book 25, Hadith 174 (FR)
Arabic reference (FR): Book 26, Hadith 183 (FR)