Sunan an-Nasa'i, Volume 1, Book 6, Hadith 591 (DarusSalam) ⓘ

It was narrated from Ibn 'Abbas that he prayed Al-Uula (Zuhr) and 'Asr together in Al-Basrah with nothing in between them, and he prayed Maghrib and 'Isha' together with nothing in between them. He did that because he was busy and Ibn 'Abbas said that he had prayed Zuhr and 'Isha' together with the Messenger of Allah in Al-Madinah, eight Rak'ahs with nothing in between.

أَخْبَرَنَا أَبُو عَاصِمٍ، خُشَيْشُ بْنُ أَصْرَمَ قَالَ حَدَّثَنَا حَبَّانُ بْنُ هِلاَلٍ، حَدَّثَنَا حَبِيبٌ، - وَهُوَ ابْنُ أَبِي حَبِيبٍ - عَنْ عَمْرِو بْنِ هَرِمٍ، عَنْ جَابِرِ بْنِ زَيْدٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّهُ صَلَّى بِالْبَصْرَةِ الأُولَى وَالْعَصْرَ لَيْسَ بَيْنَهُمَا شَىْءٌ وَالْمَغْرِبَ وَالْعِشَاءَ لَيْسَ بَيْنَهُمَا شَىْءٌ فَعَلَ ذَلِكَ مِنْ شُغْلٍ وَزَعَمَ ابْنُ عَبَّاسٍ أَنَّهُ صَلَّى مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم بِالْمَدِينَةِ الأُولَى وَالْعَصْرَ ثَمَانِ سَجَدَاتٍ لَيْسَ بَيْنَهُمَا شَىْءٌ ‏.‏