Surah Al-Qasas 28:11

وَقَالَتْ لِأُخْتِهِۦ قُصِّيهِ ۖ فَبَصُرَتْ بِهِۦ عَن جُنُبٍ وَهُمْ لَا يَشْعُرُونَ

And she said to his sister, "Follow him"; so she watched him from a distance while they perceived not.

Translation: Saheeh International

Tafsir

And she said to his sister Mary ‘Follow him’ in other words follow where he goes in order to find out his news. So she watched him from afar from a distance secretly while they were not aware that she was his sister or that she was even watching him.

Excerpt from Tafsir al-Jalalayn, commentary on 28:11, via Quran.com. The reader has the full commentary and 9 more tafsirs.