Surat Al-A'raaf (The Heights) - الأعراف

وَوَٰعَدْنَا مُوسَىٰ ثَلَٰثِينَ لَيْلَةً وَأَتْمَمْنَٰهَا بِعَشْرٍ فَتَمَّ مِيقَٰتُ رَبِّهِۦٓ أَرْبَعِينَ لَيْلَةً وَقَالَ مُوسَىٰ لِأَخِيهِ هَٰرُونَ ٱخْلُفْنِى فِى قَوْمِى وَأَصْلِحْ وَلَا تَتَّبِعْ سَبِيلَ ٱلْمُفْسِدِينَ ﴿١٤٢﴾

And We appointed with Musa a time of thirty nights and completed them with ten (more), so the appointed time of his Lord was complete forty nights, and Musa said to his brother Haroun: Take my place among my people, and act well and do not follow the way of the mischief-makers.