Muwatta Malik 20

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

Reference

Muwatta Malik 20

In-book

Book 1, Hadith 20