Sunan Abi Dawud Book 4, Hadith 20
Abdullah ibn Dinar said: The sun set when I was with Abdullah ibn Umar. We proceeded, and when we saw that the evening came, we said prayer. He went on travelling until the twilight disappeared and the stars became thick. He then slighted and combined the two prayers. Then he said: I saw the Messenger of Allah (ﷺ); when he hastened his travelling, he would pray like this prayer of mine. He said: He would combine the two prayers after the passing of a part of night. AbuDawud said: This has been transmitted by Asim ibn Muhammad from his brother on the authority of Salim and this has also been narrated by Ibn AbuNajih from Isma'il ibn AbdurRahman ibn Dhuwayb saying that Ibn Umar would combine the two prayers after the disappearance of twilight.
There was a distance of ten miles between them, that is, Mecca and Sarif.
When the Messenger of Allah (ﷺ) proceeded before the sun had declined, he delayed the noon prayer till the time of the afternoon prayer, he would then alight and combine the two prayers. If the sun declined before he moved off, he would offer the noon prayer and rode (the beast) - may peace be upon him.
Abu Dawud said: The narrator Mufaddal was the judge of Egypt. His supplication was accepted by Allah; he was the son of Fudalah.