Bismillaah Al-Hamdulillaah wa salatu wa salaamu 'ala rasulullaah
Amma-ba'd
Eating Cucumber with Fresh Dates is a Sunnah
Imam Ahmad recorded in his Musnad: Ibraaheem ibn Sa'd narrated to us from his father from 'Abdullaah ibn Ja'far (radiallaahu 'anhu), who said: I saw the Prophet (salallaahu 'alaihi wa sallam) eating cucumber with fresh dates.
(Musnad Ahmad, Vol. 1, p. 203. The Isnaad of this hadeeth is saheeh according to the conditions set by al-Bukhaaree and Muslim.)
Taken from: Imam Ahmad's Thulaathiyyaat, which are the 300+ ahadeeth that Imam Ahmad recorded with only three narrators between him and the Prophet, sallallaahu 'alayhi wa sallam.