Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
quran:36:16 –

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

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˺!
القرآن:٣٦:١٦ –

قَالُوا رَبُّنَا يَعْلَمُ إِنَّا إِلَيْكُمْ لَمُرْسَلُونَ  

{قالوا ربنا يعلم} جار مجرى القسم، وزيد التأكيد به وباللام على ما قبله لزيادة الإنكار في {إنا إليكم لمرسلون}.