Mutual agreement in various transactions is attained when both parties have the right to uphold or dissolve the agreement before they part. In the Two Sahihs, it is recorded that the Messenger of Allah said,

«الْبَيِّعَانِ بِالْخِيَارِ مَالَمْ يَتَفَرَّقَا»

(The seller and the buyer retain the (right to change their mind) as long as they have not parted.) Al-Bukhari's wording for this Hadith reads,

«إِذَا تَبَايَعَ الرَّجُلانِ فَكُلُّ وَاحِدٍ مِنْهُمَا بِالْخِيَارِ، مَالَمْ يَتَفَرَّقَا»

(When two men conduct a transaction, they retain their (right to change their mind) as long as they have not parted.)