Conditions of As-Salam sale
9-1-2014 | IslamWeb
Question:
Dear Shaykh, please explain the following: a condition of As-Salam (advance payment sale) is that it has a definite description. What does this mean?
Answer:
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, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
As-Salam is one of the permissible sales, whereby a commodity of a definite description is sold for cash that is paid later. A condition of this sale is that the commodity should be delivered after a specific period of time. Al-Bukhari, may Allaah Have mercy upon him, had a chapter in his Saheeh entitled “A chapter on As-Salam to a term.”
The majority of scholars stated a ‘specified term for delivery’ as a condition of the validity for this sale. This is because the Prophet, sallallaahu ‘alayhi wa sallam, said: “Whoever makes Salam sale, let him do that with a known specified measure or a known specified weight and for a known specified period.” [Al-Bukhari and Muslim]
In Al-Mughni, Ibn Qudaamah 
said: "The Prophet, sallallaahu ‘alayhi wa sallam, commanded that a definite term must be specified and his command entails obligation. His commands here are to explain the conditions of the Salam sale without which that kind of sale will be forbidden. Hence, this sale will be invalid if the measure and weight are not specified and similarly if the term is not specified."
The Shaafi‘i scholars permitted the immediate Salam, and said, “If it is permissible for a delayed term while involving uncertainty, then it will be more permissible for an immediate term.”