And remember We appointed forty nights for Moses, and in his absence ye took the calf (for worship), and ye did grievous wrong. (2:51)

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." (7:142)