Abu Dawud
Prayer
Book Number: 002 / Hadith Number: 579
Narated By 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 (pbuh) say: Do not say a prayer twice in a day.