18:61
فَلَمَّا بَلَغَا مَجْمَعَ بَيْنِهِمَا نَسِيَا حُوتَهُمَا فَٱتَّخَذَ سَبِيلَهُۥ فِى ٱلْبَحْرِ سَرَبًا
But when they reached the junction between them, they forgot their fish, and it took its course into the sea, slipping away.
The Cave
فَلَمَّا بَلَغَا مَجْمَعَ بَيْنِهِمَا نَسِيَا حُوتَهُمَا فَٱتَّخَذَ سَبِيلَهُۥ فِى ٱلْبَحْرِ سَرَبًا
But when they reached the junction between them, they forgot their fish, and it took its course into the sea, slipping away.
Nearby ayahs help place verse 18:61 in sequence and meaning.
وَتِلْكَ ٱلْقُرَىٰٓ أَهْلَكْنَـٰهُمْ لَمَّا ظَلَمُوا۟ وَجَعَلْنَا لِمَهْلِكِهِم مَّوْعِدًا
And those cities - We destroyed them when they wronged, and We made for their destruction an appointed time.
وَإِذْ قَالَ مُوسَىٰ لِفَتَىٰهُ لَآ أَبْرَحُ حَتَّىٰٓ أَبْلُغَ مَجْمَعَ ٱلْبَحْرَيْنِ أَوْ أَمْضِىَ حُقُبًا
And [mention] when Moses said to his servant, "I will not cease [traveling] until I reach the junction of the two seas or continue for a long period."
فَلَمَّا جَاوَزَا قَالَ لِفَتَىٰهُ ءَاتِنَا غَدَآءَنَا لَقَدْ لَقِينَا مِن سَفَرِنَا هَـٰذَا نَصَبًا
So when they had passed beyond it, [Moses] said to his boy, "Bring us our morning meal. We have certainly suffered in this, our journey, [much] fatigue."
قَالَ أَرَءَيْتَ إِذْ أَوَيْنَآ إِلَى ٱلصَّخْرَةِ فَإِنِّى نَسِيتُ ٱلْحُوتَ وَمَآ أَنسَىٰنِيهُ إِلَّا ٱلشَّيْطَـٰنُ أَنْ أَذْكُرَهُۥ ۚ وَٱتَّخَذَ سَبِيلَهُۥ فِى ٱلْبَحْرِ عَجَبًا
He said, "Did you see when we retired to the rock? Indeed, I forgot [there] the fish. And none made me forget it except Satan - that I should mention it. And it took its course into the sea amazingly".