Sahih Muslim Book 8, Hadith Number 3302.

Chapter: Fulfilling of condition in marriage.

‘Uqba b. Amir (Allah be pleased with him) reported Allah’s Messenger (May peace be upon him) as saying: The most worthy condition which must be fulfilled is that which makes sexual intercourse lawful. In the narration transmitted by Ibn Muthanna (instead of the word “condition”) it is “conditions”.