Prayer (Kitab Al-Salat)
Dawud :: Book 2 : Hadith 530
Narrated Umm Salamah, Ummul Mu'minin:
The Apostle of Allah (peace_be_upon_him) taught me to say when the adhan for the sunset prayer was called; "O Allah, this is the time when Thy night comes on, Thy day retires, and the voices of Thy summoners are heard, so forgive me."