Shama-il Tirmidhi Chapter 29, Hadith Number 1 (188).

Abdullah ibn Jaafar radiyallahu anhu says, Rasoolullah sallallahu alaihe wasallam ate Qith’thaa (cucumbers) with dates.

Cucumber has a cold effect and dates have a hot one. By combining the two it becomes mild. From this hadith we gather that it is recommended that the effect (hot or cold) of things eaten should be taken into consideration. Cucumber is insipid and tasteless, and dates are sweet which results in the cucumber also tasting sweet.