Mukhtasar Sahih Bukhari — Hadith 1423

Narrated by Abu Huraira (may Allah be pleased with him) from the Noble Prophet (peace and blessings be upon him) that he (peace be upon him) said: "Khidr (peace be upon him) was named (Khidr) because he sat on a dry (barren) land (where there was no sign of greenery at all), and when he left, the land became lush and started flourishing."