Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(And when We did appoint for Moses) to spend in the mountain (thirty nights (of solitude)) the month of the Dhu'l-Qa'dah, (and added to them ten) days from the month of Dhu'l-Hijjah, (and he completed the whole time appointed by his Lord of forty nights) as he promised; (and Moses said unto his brother: Take my place) be my deputy (among the people. Do right) enjoin them to do right, (and follow not the way of mischief-makers) by committing transgressions.
And We promised Moses thirty nights, and We completed them with ten. So the appointed time of his Lord was completed in forty nights. And Moses said to his brother Aaron, “Take my place among my people.”
How exalted is making promises in friendship! How great is sitting in the promised place of friendship! How sweet is breaking promises in the religion of friendship!
Concerning the intimations of this verse the Pir of the Tariqah said, “The promises of lovers, even if broken, show intimacy.” Then he said,
“You put me off, You procrastinate,
You promise, but You don't come through.”
It is not approved to put back the promised time and to add days before the promised moment except in the religion of friendship, for in friendship disloyalty is the same as loyalty, and disdain friendship. Do you not see what the Lord of the Worlds did with Moses in this exchange? He promised him thirty days. When those passed, He added ten more. He added them because Moses was happy with that. Moses counted the thirty days as capital and the ten days as profit. He said, “Indeed, I heard the hard cash of the Real's speech for a second time when He added that.”
Come forth, by your life! Stay not away!
Give hope of your encounter, then put us off.
Promise and put off as you like,
for we love you when you put off the passionate.
If you fulfill the promise, we will be happy,
but we will live with your promise, content for a time.
In this journey, Moses waited thirty days without remembering food and drink or being aware of hunger, for he was carried by the Real in a journey of generosity, waiting for whispered prayer. The other time, when he was sent to Khiẓr on the first journey in search of knowledge, he did not have the capacity for a half day of hunger, so he said, “Bring us our food” [18:62]. This is because that was a journey of teaching courtesy and of hardship. At the beginning of the traveling he was carrying; he was not being carried. He was aware of his own suffering, for he was with himself. He saw the marks of hunger because he was in the road of creatures.
And Moses said to his brother Aaron, “Take my place among my people.” His intention was whispered prayer with the Real, so he left Aaron with the people and went alone, for there is no sharing in friendship. The friend's attribute in the path of friendship is nothing but aloneness and oneness.
If you're not busy and you're alone,
come to Me in loyalty-you're worthy of Me.
Then, when he was going to Pharaoh, he asked for Aaron's companionship: “Make him share with me in my affair” [29:32], for that was going to the creatures, and things having to do with the creatures bring aversion and dread. In carrying the burden of dread, no one flees from a kind companion and his companionship.
When Moses returned from whispered prayer and saw that the Children of Israel had left the circle of obedience and become calf-worshipers, he rebuked Aaron, not them, so that you would know that not everyone who sins is deemed worthy of rebuke. Rebuke is appropriate when a person still has something of friendship. He who burns in fear of separation is the one who recognizes the exaltation of union:
How can the Beloved's passion be suited for just anyone?
And We appointed (read wa-wā‘adnā or wa-wa‘adnā) for Moses thirty nights, at the end of which We would speak to him, after he has fasted [during that period]; that was the month of Dhū’l-Qa‘da. He completed the fast. But when it came to an end, he disliked the [bad] odour of his mouth and so cleaned his teeth. God then commanded him [to fast for] another ten nights so that He may speak to him despite the odour in his mouth: as God says, and completed them with ten, nights of Dhū’l-Hijja. Thus was the time appointed by his Lord concluded, the time at which God had promised him to speak to him, as forty (arba‘īna is a circumstantial qualifier) nights (laylatan is for specification); and Moses said to his brother Aaron, when he was departing to the Mount for the communion [with his Lord]: ‘Succeed me, be my deputy, over my people, and be righteous, [among them] with regard to their affair, and do not follow the way of the agents of corruption’, by consenting with them to acts of disobedience.
And We appointed for Moses thirty nights: it is said that He commanded him to fast for thirty [days]. Upon completing [this] he was repelled by the aftertaste in his mouth. So he cleaned his teeth, but God reprimanded for that and commanded him to add another ten days [of fasting]. It is also said that He had commanded him to seek nearness to Him with what he will do in the thirty days [in the way of fasting] and that He then revealed the Torah to him in the last [additional] ten days, thus completing forty. The first [report] alludes to that he was rid of the veil of acts, attributes and essence during the thirty days but there remained in him a remnant whose existence he could not be rid of, and so his use of the toothbrush is an allusion to the manifestation of that remnant where he says:
Allah reminds the Children of Israel of the guidance that He sent to them by speaking directly to Musa and revealing the Tawrah to him. In it, was their law and the details of their legislation. Allah stated here that He appointed thirty nights for Musa. The scholars of Tafsir said that Musa fasted this period, and when they ended, Musa cleaned his teeth with a twig. Allah commanded him to complete the term adding ten more days, making the total forty. When the appointed term finished, Musa was about to return to Mount Tur, as Allah said,
(O Children of Israel! We delivered you from your enemy, and We made a covenant with you on the right side of the Mount) 20:80. Musa left his brother Harun with the Children of Israel and commanded him to use wisdom and refrain from mischief. This was only a reminder, for Harun was an honorable and noble Prophet who had grace and exalted standard with Allah, may Allah's peace and blessings be upon him and the rest of the Prophets.
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
After their departure from Egypt, when the Israelites became free from the shackles of slavery, and won the position of an independent nation, Prophet Moses was summoned to Mount Sinai by the Divine Command so that the Law should be given to him for them. This was the first summons of the series that is being mentioned here. Forty days were appointed so that he should prepare himself by fast, devotion, worship, prayer, deep thought, meditation and reflection for the heavy task that was about to be entrusted to him On this occasion prophet Moses left the Israelites at a place now called Wadiy-u-Shaikh, between Nabi Salih and Mt. Sinai. That part of the valley where the Israelites then encamped is now called Maidan-ur-Rahat. At one end of the valley is situated the hillock, where, according to the local tradition Prophet Salih migrated from the territory of Thamud. The mosque, which was built in his memory, stands there even today. On the other side, there is another hillock, called Jabl-i-Harun, where, it is said, Prophet Aaron had gone in protest against the cow-worship of the Israelites. On its third side is Mt. Sinai, which is 7359 feet above the sea level and is usually covered with clouds. On the top of this is the cave in which Moses spent forty days and nights and which has become a holy place of pilgrimage. There is a mosque of the Muslims and a church of the Christians near the cave and at the foot, a monastery built during the reign of Justinian, Byzantine Emperor. (For details, see E.N.'s 9, 10 of XXVIII).
Though Prophet Aaron was the elder of the two by three years, he was under Prophet Moses in the mission of Prophethood. In fact, Prophet Aaron was appointed as a Prophet to work as an assistant to Moses in response to his prayer. The fact that he was appointed by Allah as assistant to Prophet Moses has. been stated in XXV: 35.