Al-A'raf 7:142

۞ وَوَٰعَدْنَا مُوسَىٰ ثَلَٰثِينَ لَيْلَةًۭ وَأَتْمَمْنَٰهَا بِعَشْرٍۢ فَتَمَّ مِيقَٰتُ رَبِّهِۦٓ أَرْبَعِينَ لَيْلَةًۭ ۚ وَقَالَ مُوسَىٰ لِأَخِيهِ هَٰرُونَ ٱخْلُفْنِى فِى قَوْمِى وَأَصْلِحْ وَلَا تَتَّبِعْ سَبِيلَ ٱلْمُفْسِدِينَ

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."