Bai Salam (Arabic بيع سلم, more accurately transliterated as Bai us Salami) is an Islamic contract in which full payment is made in advance for specific goods (often agricultural products) to be delivered at a future date.
It is necessary that the quality of the commodity intended to be purchased is fully specified leaving no ambiguity leading to dispute.
Bai salam covers almost every thing which is capable of being definitely described as to quality, quantity and workmanship.
Salam sale is an exception found in the hadith of the prophet of Islam Muhammad (collections of his sayings and teachings) provided the goods are defined and the date of delivery is fixed.
[3] Upon migration from Makkah, Mohammed came to Madinah, where the people used to pay in advance the price of fruit or dates to be delivered over one, two or three years.