Sahih Muslim Book 6, Hadith Number 2450.
Chapter : Kissing is not forbidden while fasting if one is not urged by sexual lust.
Umar b Abu Salama reported that he asked the Messenger of Allah (may peace be upon him): Should one observing fast kiss (his wife)? The Messenger of Allah (may peace be upon him) said to him: Ask her (Umm Salama). She informed him that the Messenger of Allah (may peace be upon him) did that, where upon he said: Messenger of Allah, Allah pardoned thee all thy sins, the previous and the later ones. Upon this the Messenger of Allah (may peace be upon him)) said: By Allah, I am the most God conscious among you and I fear Him most among you.