‘Abdullah bin ‘Umar (may Allah be pleased with both of them) says: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say:“The seller and the buyer both have the option (to cancel or confirm the sale) as long as they have not separated, or they both stipulate the option.”Nafi‘ says: When Ibn ‘Umar (may Allah be pleased with both of them) would buy something and was sitting, he would stand up so that the sale would become binding (and the option would no longer remain).

Imam Tirmidhi says:
1- The hadith of Ibn ‘Umar (may Allah be pleased with both of them) is Hasan Sahih.
2- In this chapter, there are also ahadith from Abu Barzah, Hakim bin Hizam, ‘Abdullah bin ‘Abbas, ‘Abdullah bin ‘Amr, Samurah, and Abu Hurairah (may Allah be pleased with them).
3- Some of the people of knowledge from among the Companions and others have acted upon this. And this is also the saying of Shafi‘i, Ahmad, and Ishaq bin Rahwayh. These people say that by separation is meant physical separation, not verbal separation, i.e., leaving the gathering is meant, not changing the subject of conversation.
4- And some of the people of knowledge say that by the saying of the Prophet (peace and blessings of Allah be upon him) «مالم يتفرقا» is meant verbal separation. The first opinion is more correct, because Ibn ‘Umar (may Allah be pleased with both of them) himself narrated this from the Prophet (peace and blessings of Allah be upon him), and he knows best the meaning of the hadith he narrated. And it is narrated from him that when he intended to make the sale binding, he would (leave the gathering and) walk away so that the sale would become binding.
5- It is also narrated in the same way from Abu Barzah (may Allah be pleased with him).