It was narrated that Ibn 'Abbas (رضي الله عنه) said:

When The Messenger of Allah (ﷺ) came (to Madinah), they used to pay one or two years in advance for dates, or two or three years. The Messenger of Allah (ﷺ) said: "Pay in advance for dates for a specified measure and a specified weight, (to be delivered) at a specified time.”