Sahih Muslim 2380 f
'Utba b. Mas, ud reported that 'Abdullah b. 'Abbas contended with Hurr b. Qais b. Hisn al-Fazari aboat the companion of Moses (peace be upon hiin). Ibn 'Abbas said that he was Khadir. There happened to pass Ubayy b. Ka'b Ansari. Ibn Abbas called him and said:
Abu Tufail, come to us. There has been a difference of opinion between me and my friend about the companion of Moses whom he wanted to meet on the way. Did hear anything from Allah's meesenger (ﷺ) making a mention of anything? Ubayy said: I heard Allah's Messenger (may Peace be upon him) as saying: As Moses was amongst the group of Bani Isra'il, there came to him a person and he said to him: Do you know anyone having better knowledge than you? Moses said: No. Thereupon Allah revealed to Moses: Of course, there is amongst Our servants Khadir (who has better knowledge) than you. Moses asked the way of meeting him. Allah made the fish a sign and it was said to him: Where you miss the fish return to that (place) and you will soon find him. So Moses moved on as Allah wished him to move on. He then said to his young companion: Bring for us the breakfast. Thereupop that young man said to Moses. when he asked him for the breakfast: Don't you see that as we had reached the Sakhra I forgot the fish and nobody made it forget (in our mind) but the satan that I should remind you of it? Mosed said to that young man: This was what we wanted. So they retraced their steps and met Khadir and the events which followed have been described in His Book except that Yunus (the narrator) said that he followed the traces of fish in the ocean.
حَدَّثَنِي حَرْمَلَةُ بْنُ يَحْيَى، أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي يُونُسُ، عَنِ ابْنِ شِهَابٍ، عَنْ 
 عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ بْنِ مَسْعُودٍ، عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، أَنَّهُ تَمَارَى هُوَ وَالْحُرُّ
 بْنُ قَيْسِ بْنِ حِصْنٍ الْفَزَارِيُّ فِي صَاحِبِ مُوسَى عَلَيْهِ السَّلاَمُ فَقَالَ ابْنُ عَبَّاسٍ هُوَ الْخَضِرُ
 ‏.‏ فَمَرَّ بِهِمَا أُبَىُّ بْنُ كَعْبٍ الأَنْصَارِيُّ فَدَعَاهُ ابْنُ عَبَّاسٍ فَقَالَ يَا أَبَا الطُّفَيْلِ هَلُمَّ إِلَيْنَا فَإِنِّي
 قَدْ تَمَارَيْتُ أَنَا وَصَاحِبِي هَذَا فِي صَاحِبِ مُوسَى الَّذِي سَأَلَ السَّبِيلَ إِلَى لُقِيِّهِ فَهَلْ سَمِعْتَ
 رَسُولَ اللَّهِ صلى الله عليه وسلم يَذْكُرُ شَأْنَهُ فَقَالَ أُبَىٌّ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه
 وسلم يَقُولُ ‏
"‏ بَيْنَمَا مُوسَى فِي مَلإٍ مِنْ بَنِي إِسْرَائِيلَ إِذْ جَاءَهُ رَجُلٌ فَقَالَ لَهُ هَلْ تَعْلَمُ أَحَدًا
 أَعْلَمُ مِنْكَ قَالَ مُوسَى لاَ ‏.‏ فَأَوْحَى اللَّهُ إِلَى مُوسَى بَلْ عَبْدُنَا الْخَضِرُ - قَالَ - فَسَأَلَ
 مُوسَى السَّبِيلَ إِلَى لُقِيِّهِ فَجَعَلَ اللَّهُ لَهُ الْحُوتَ آيَةً وَقِيلَ لَهُ إِذَا افْتَقَدْتَ الْحُوتَ فَارْجِعْ فَإِنَّكَ
 سَتَلْقَاهُ فَسَارَ مُوسَى مَا شَاءَ اللَّهُ أَنْ يَسِيرَ ثُمَّ قَالَ لِفَتَاهُ آتِنَا غَدَاءَنَا ‏.‏ فَقَالَ فَتَى مُوسَى
 حِينَ سَأَلَهُ الْغَدَاءَ أَرَأَيْتَ إِذْ أَوَيْنَا إِلَى الصَّخْرَةِ فَإِنِّي نَسِيتُ الْحُوتَ وَمَا أَنْسَانِيهُ إِلاَّ الشَّيْطَانُ
 أَنْ أَذْكُرَهُ ‏.‏ فَقَالَ مُوسَى لِفَتَاهُ ذَلِكَ مَا كُنَّا نَبْغِي ‏.‏ فَارْتَدَّا عَلَى آثَارِهِمَا قَصَصًا فَوَجَدَا
 خَضِرًا ‏.‏ فَكَانَ مِنْ شَأْنِهِمَا مَا قَصَّ اللَّهُ فِي كِتَابِهِ ‏"‏ ‏.‏ إِلاَّ أَنَّ يُونُسَ قَالَ فَكَانَ يَتَّبِعُ أَثَرَ
 الْحُوتِ فِي الْبَحْرِ ‏.‏