Sunan of Abu Dawood Book 4, Hadith 1217

حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ شُعَيْبٍ، حَدَّثَنَا ابْنُ وَهْبٍ، عَنِ اللَّيْثِ، قَالَ قَالَ رَبِيعَةُ - يَعْنِي كَتَبَ إِلَيْهِ - حَدَّثَنِي عَبْدُ اللَّهِ بْنُ دِينَارٍ قَالَ غَابَتِ الشَّمْسُ وَأَنَا عِنْدَ عَبْدِ اللَّهِ بْنِ عُمَرَ فَسِرْنَا فَلَمَّا رَأَيْنَاهُ قَدْ أَمْسَى قُلْنَا الصَّلاَةُ ‏.‏ فَسَارَ حَتَّى غَابَ الشَّفَقُ وَتَصَوَّبَتِ النُّجُومُ ثُمَّ إِنَّهُ نَزَلَ فَصَلَّى الصَّلاَتَيْنِ جَمِيعًا ثُمَّ قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم إِذَا جَدَّ بِهِ السَّيْرُ صَلَّى صَلاَتِي هَذِهِ يَقُولُ يَجْمَعُ بَيْنَهُمَا بَعْدَ لَيْلٍ ‏.‏ قَالَ أَبُو دَاوُدَ رَوَاهُ عَاصِمُ بْنُ مُحَمَّدٍ عَنْ أَخِيهِ عَنْ سَالِمٍ وَرَوَاهُ ابْنُ أَبِي نَجِيحٍ عَنْ إِسْمَاعِيلَ بْنِ عَبْدِ الرَّحْمَنِ بْنِ ذُؤَيْبٍ أَنَّ الْجَمْعَ بَيْنَهُمَا مِنِ ابْنِ عُمَرَ كَانَ بَعْدَ غُيُوبِ الشَّفَقِ ‏.‏

Narrated Abdullah ibn Umar: 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