Hadith 114
قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " إِنَّمَا سُمِّيَ الْخَضِرُ لأَنَّهُ جَلَسَ عَلَى فَرْوَةٍ بَيْضَاءَ، فَإِذَا هِيَ تَهْتَزُّ تَحْتَهُ خَضْرَاءَ "
And the Messenger of Allah, peace and blessings be upon him, said: "Khidr was named «خضر» because once he sat on white sand or dry land, and suddenly that land beneath him turned lush and green, waving with vegetation."