مُوَطَّأُ مَالِكٍ
Muwatta Malik 20
The Times of Prayer
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ دَاوُدَ بْنِ الْحُصَيْنِ، قَالَ أَخْبَرَنِي مُخْبِرٌ، أَنَّ عَبْدَ اللَّهِ بْنَ عَبَّاسٍ، كَانَ يَقُولُ دُلُوكُ الشَّمْسِ إِذَا فَاءَ الْفَىْءُ وَغَسَقُ اللَّيْلِ اجْتِمَاعُ اللَّيْلِ وَظُلْمَتُهُ .
Yahya related to me from Malik that Da'ud ibn al-Husayn said that someone had told him Abdullah ibn Abbas used to say, "Duluk ash-shams begins from when the sun passes the meridian. Ghasaq al-layl is the gathering of the night and its darkness."
Arabic/English book reference: Book 1, Hadith 20