"And We made an appointment with Moses for thirty nights and perfected them with ten [more]," and they are: Dhu al-Qa'dah and the ten [nights] of Dhu al-Hijjah.
Al-Kalbi said:
When Moses had crossed the sea with the Children of Israel, and Allah had drowned the people of Pharaoh, the Children of Israel said to Moses: O Moses, bring us a Book from our Lord as You promised us, for you claimed that you would bring it to us within a month. So Moses chose seventy men from his people to accompany him. When they had prepared themselves, Allah said: O Moses, inform your people that you will not come to them for forty nights. That was when it was completed with the ten. When Moses departed with the seventy, he commanded them to wait for him.
﴿وَوَاعَدْنَا مُوسَى ثَلاثِينَ لَيْلَةً وَأَتْمَمْنَاهَا بِعشر﴾ وَهِيَ: ذُو الْقِعْدَةُ وَعَشْرُ ذِي الْحِجَّةِ.
قَالَ الْكَلْبِيُّ:
إِنَّ مُوسَى لَمَّا قَطَعَ الْبَحْرَ بِبَنِي إِسْرَائِيلَ، وَغَرَّقَ اللَّهُ آلَ فِرْعَوْنَ - قَالَتْ بَنُو إِسْرَائِيلَ لِمُوسَى: يَا مُوسَى، ائْتِنَا بكتابٍ مِنْ رَبِّنَا كَمَا وَعَدْتَنَا، وَزَعَمْتَ أَنَّكَ تَأْتِينَا بِهِ إِلَى شَهْرٍ، فَاخْتَارَ مُوسَى مِنْ قَوْمِهِ سَبْعِينَ رَجُلًا لِيَنْطَلِقُوا مَعَهُ، فَلَمَّا تَجَهَّزُوا قَالَ اللَّهُ: يَا مُوسَى، أَخْبِرْ قَوْمَكَ أَنَّكَ لَنْ تَأْتِيَهُمْ أَرْبَعِينَ لَيْلَةً. وَذَلِكَ حِينَ تَمَّتْ بعشرٍ، فَلَمَّا خَرَجَ مُوسَى بِالسَّبْعِينَ أَمْرَهُمْ أَنْ يَنْتَظِرُوهُ
