Sahih al-Bukhari 2240.2

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 2240.2

In-book

Book 35, Hadith 4

English

Muhsin Khan