كتاب البيوع
Read the English translation first, with the original Arabic directly underneath.
It was narrated from Yahya bin Sa 'eed who said:
"I heard Nafi narrating from Ibn 'Umar, form the Messenger of Allah '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."
إِنَّ الْمُتَبَايِعَيْنِ بِالْخِيَارِ فِي بَيْعِهِمَا مَا لَمْ يَفْتَرِقَا إِلاَّ أَنْ يَكُونَ الْبَيْعُ خِيَارًا