It was narrated from Yahya bin Sa 'eed who said: "I heard Nafi narrating from Ibn 'Umar, form the Messenger of Allah (ﷺ) 'the two parties to a transaction both have the choice so long as they have not separated unless they have chosen to conclude the transaction. " Nafi said: ''When 'Abdullah bought something he like, he would leave straightaway."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا عَبْدُ الْوَهَّابِ، قَالَ سَمِعْتُ يَحْيَى بْنَ سَعِيدٍ، يَقُولُ سَمِعْتُ نَافِعًا، يُحَدِّثُ عَنِ ابْنِ عُمَرَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم " إِنَّ الْمُتَبَايِعَيْنِ بِالْخِيَارِ فِي بَيْعِهِمَا مَا لَمْ يَفْتَرِقَا إِلاَّ أَنْ يَكُونَ الْبَيْعُ خِيَارًا " . قَالَ نَافِعٌ فَكَانَ عَبْدُ اللَّهِ إِذَا اشْتَرَى شَيْئًا يُعْجِبُهُ فَارَقَ صَاحِبَهُ .
sunnah.com