Abu Dawud Book 2, Hadith Number 1206.
Chapter : On the combination of two prayers at a time.
Narated By ‘Abd Allah b. ‘Abbas : The Apostle of Allah (PBUH) combined the noon and the afternoon prayers, and combined the sunset and the night prayers without any danger or journey. Malik said: I think it so happened during rain.
Abu Dawud said: Hammad b. Salamah narrated in a like manner from Abu al-Zubair; it has been narrated by Qurrah b. Khalid from Abu al-Zubair. He said: It so happened in a journey that we made to Tabuk.