From Sahih Bukhari (Hadith 5213):
Narrated Anas:The tradition, (of the Prophet) is that if someone marries a virgin and he has already a matron wife (with him), then he should stay with the virgin for seven days; and if someone marries a matron (and he has already a virgin wife with him) then he should stay with her for three days
Reference: Bukhari 5213