Surah Al-Kahf 18:64

قَالَ ذَٰلِكَ مَا كُنَّا نَبْغِ ۚ فَٱرْتَدَّا عَلَىٰٓ ءَاثَارِهِمَا قَصَصًا

[Moses] said, "That is what we were seeking." So they returned, following their footprints.

Translation: Saheeh International

Tafsir

Said he Moses ‘That namely our losing the fish is what we have been seeking!’ what we have been after for it is a sign for us of the presence of the one whom we seek. So they turned back retracing their footsteps until they reached the rock.

Excerpt from Tafsir al-Jalalayn, commentary on 18:64, via Quran.com. The reader has the full commentary and 9 more tafsirs.