It was narrated from Ibn 'Umar,:
from the Prophet, concerning a man who had a wife then divorced her, then another man married her but divorced her before consummating the marriage. Could she go back to the first man? He said: "No, not until he tastes her sweetness." (ID)
English reference (ID): Vol. 3, Book 9, Hadith 1933 (ID)
Arabic reference (ID): Book 9, Hadith 2008 (ID)