Surah Al-Qasas 28:13

فَرَدَدْنَـٰهُ إِلَىٰٓ أُمِّهِۦ كَىْ تَقَرَّ عَيْنُهَا وَلَا تَحْزَنَ وَلِتَعْلَمَ أَنَّ وَعْدَ ٱللَّهِ حَقٌّ وَلَـٰكِنَّ أَكْثَرَهُمْ لَا يَعْلَمُونَ

So We restored him to his mother that she might be content and not grieve and that she would know that the promise of Allāh is true. But most of them [i.e., the people] do not know.

Translation: Saheeh International

Tafsir

Thus We restored him to his mother so that her eyes might delight in seeing him again and not grieve thereat and that she might know that God’s promise to restore him to her is true; but most of them that is the people do not know about this promise or of the fact that this was his sister and the other was his mother. …

Excerpt from Tafsir al-Jalalayn, commentary on 28:13, via Quran.com. The reader has the full commentary and 9 more tafsirs.