Sahih Bukhari
Times of the Prayers
Volume: 001 / Book Number: 010 / Hadith Number: 518
Narrated Ibn 'Abbas:
"The Prophet prayed eight Rakat for the Zuhr and 'Asr, and seven for the Maghrib and 'Isha prayers in Medina." Aiyub said, "Perhaps those were rainy nights." Anas said, "May be."