Surah Al-A'raf (The Heights), Verse 142

وَوٰعَدْنَا مُوْسٰی ثَلٰثِیْنَ لَیْلَةً وَّاَتْمَمْنٰهَا بِعَشْرٍ فَتَمَّ مِیْقَاتُ رَبِّهٖۤ اَرْبَعِیْنَ لَیْلَةً وَقَالَ مُوْسٰی لِاَخِیْهِ هٰرُوْنَ اخْلُفْنِیْ فِیْ قَوْمِیْ وَاَصْلِحْ وَلَا تَتَّبِعْ سَبِیْلَ الْمُفْسِدِیْنَ ۟

Wa waa'adnaa Moosaa salaaseena lailatanw wa at mamnaahaa bi'ashrim fatamma meeqaatu Rabbihee arba'eena lailah; wa qaala Moosaa liakheehi Haaroonakh lufnee fee qawmee wa aslih wa laa tattabi' sabeelal mufsideen

“We appointed for Moses thirty nights, and completed (the period) with ten (more): thus was completed the term (of communion) with his Lord, forty nights. And Moses had charged his brother Aaron (before he went up): "Act for me amongst my people: Do right, and follow not the way of those who do mischief."”

Quran 7:142 (Yusuf Ali Translation)