حَدَّثَنَا عَلِيٌّ، حَدَّثَنَا سُفْيَانُ، قَالَ حَدَّثَنِي ابْنُ أَبِي نَجِيحٍ، وَقَالَ، فَلْيُسْلِفْ فِي كَيْلٍ مَعْلُومٍ إِلَى أَجَلٍ 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 : Book 35, Hadith 4
USC-MSA web (English) : Vol. 3, Book 35, Hadith 444 (deprecated)