Abu Dawud
Fasting
Book Number: 007 / Hadith Number: 2381
Narated By AbuHurayrah : A man asked the Prophet (pbuh) whether one who was fasting could embrace (his wife) and he gave him permission; but when another man came to him, and asked him, he forbade him. The one to whom he gave permission was an old man and the one whom he forbade was a youth.