what mean istihsaan? with practical examples in sales if possible?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Al-Istihsaan means departing from a ruling of Qiyas (analogy) in a certain case, in a manner that is different from the way similar cases have been decided on the basis of the Quran, Sunnah (Prophetic tradition) or Ijmaa' (consensus of the scholars). This preference is exercised in order to achieve a more equitable solution because of the rigidity or unfairness that is brought about by strict adherence to the existing law.

An example for this would be the sale of ‘Araaya, which are palm trees, the fruits of which have been given as a gift. The Sharee’ah (Islamic law) permits the owner (the recipient of the gift) to sell his ‘Araaya on the tree by way of estimation, with the condition that such fruit does not exceed 5 Awsuq (pl., Wasaq, i.e. 300 Saa’s, which equals 653 kg [according to the view of the majority of the scholars] [1 Wasaq is 130.56 kg])

In principle, this involves Riba (interest and or usury) because it is selling one type [of dates] in return for the like of it with interest (an increment), but this was made permissible due to the existence of an Islamic text as the Prophet permitted selling ‘Araaya. [Al-Bukhari and Muslim]

Therefore, this is leaving the principle because of Istihsaan, and this is called Al-Istihsaan due to the existence of (an Islamic) text.

Another example of Al-Istihsaan is what is called Khiyaar An-Naqd for those who permitted it among the scholars. The Book of Islamic Fiqh and its Evidences authored by Dr. Wahbah Az-Zuhaili reads, “Khiyaar An-Naqd is a term used to express an option within a certain period after the conclusion of a bargain during which the seller has the option to cancel the contract if the buyer does not pay in cash up to a certain agreed date.

But if the buyer pays the price during the given period, then the sale is concluded, and if he does not pay during this period, the sale is invalidated."

On the other hand, Abu Haneefah and his two disciples, contrarily to Zufar, permitted Khiyaar An-Naqd as a way of Istihsaan due to people's need for it in reality, and because it is in essence a kind of conditioing the choice of breaking the contract (by either party). What supports this as well is that Ibn ‘Umar permitted it.

Allaah Knows best.