وَوَاعَدْنَا مُوسَى ثَلاَثِينَ لَيْلَةً وَأَتْمَمْنَاهَا بِعَشْرٍ فَتَمَّ مِيقَاتُ رَبِّهِ أَرْبَعِينَ لَيْلَةً وَقَالَ مُوسَى لأَخِيهِ هَارُونَ اخْلُفْنِي فِي قَوْمِي وَأَصْلِحْ وَلاَ تَتَّبِعْ سَبِيلَ الْمُفْسِدِينَ
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سورة الأعراف
(7/142) And We treated with Musa thirty nights, and We completed them with ten; so the appointment of his Lord was completed by forty nights. And Musa said unto his brother Harun: act thou in my place among my people, and rectify, and follow not the way of the corrupters.
Surah Al-A'raf