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. (ID)
English reference (ID): Book 25, Hadith 174 (ID)
Arabic reference (ID): Book 26, Hadith 183 (ID)