Prayer (Kitab Al-Salat)
Dawud :: Book 2 : Hadith 579
Narrated Abdullah ibn Umar:
Sulayman, the freed slave of Maymunah, said: I came to Ibn Umar at Bilat (a place in Medina) while the people were praying. I said: Do you not pray along with them? He said: I heard the Apostle of Allah (peace_be_upon_him) say: Do not say a prayer twice in a day.