Sahih Bukhari Volume 4, Book 55, Hadith Number 615.

Narated By Abu Huraira : Allah’s Apostle said, “It was said to Bani Israel, Enter the gate (of the town) with humility (prostrating yourselves) and saying: “Repentance”, but they changed the word and entered the town crawling on their buttocks and saying: “A wheat grain in the hair.”