(2) باب السَّلَمِ فِي وَزْنٍ مَعْلُومٍ
Narrated Ibn Abi Najih:
as above, saying, "He should pay the price in advance for a specified measure and for a specified period."
Reference: Sahih al-Bukhari 2240
In-book reference: Book 35, Hadith 4
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 35, Hadith 444