﴿ وَإِذْ قَالَ مُوسَىٰ لِفَتَىٰهُ لَآ أَبْرَحُ حَتَّىٰٓ أَبْلُغَ مَجْمَعَ ٱلْبَحْرَيْنِ أَوْ أَمْضِىَ حُقُبًۭا ﴾

“AND LO! [In the course of his wanderings,] Moses said to his servant: "I shall not give up until I reach the junction of the two seas, even if I [have to] spend untold years [in my quest]!"”

Please check ayah 18:65 for complete tafsir.