Surah Ya-Sin 36:16

قَالُوا۟ رَبُّنَا يَعْلَمُ إِنَّآ إِلَيْكُمْ لَمُرْسَلُونَ

They said, "Our Lord knows that we are messengers to you,

Translation: Saheeh International

Tafsir

They said ‘Our Lord knows qālū rabbunā ya‘lamu functions like an oath. Emphasis is intensified by this oath and also by the addition of the lām to what was before simply mursalūna ‘we have been sent’ to counter their intensified denial that we have indeed been sent to you by Him!

Excerpt from Tafsir al-Jalalayn, commentary on 36:16, via Quran.com. The reader has the full commentary and 9 more tafsirs.