Sahih Bukhari Volume 7, Book 62, Hadith Number 78.

Narrated By Anas : Abdur Rahman bin ‘Auf married a woman and gave her gold equal to the weight of a date stone (as Mahr). When the Prophet noticed the signs of cheerfulness of the marriage (on his face) and asked him about it, he said, “I have married a woman and gave (her) gold equal to a date stone in weight (as Mahr).”