Sunan an-Nasa'i 4474
It was narrated from Yahya bin Sa 'eed , who said:
"Nafi narrated   to us from Ibn 'Umar, who said: 'The Messenger of Allah said: There is no transaction between the two parties until they separate, unless they have chosen to conclude the transaction."" (Sahih )
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا هُشَيْمٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، قَالَ حَدَّثَنَا نَافِعٌ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ الْمُتَبَايِعَانِ لاَ بَيْعَ بَيْنَهُمَا حَتَّى يَتَفَرَّقَا إِلاَّ بَيْعَ الْخِيَارِ ‏"‏ ‏.‏