Al-Muzzammil 73:20

Indeed, your Lord knows that you [O Prophet] stand up in prayer for nearly two-thirds of the night, or half of it, or one-third of it, as do others among your companions. Allah determines the night and the day; He knows that you [Muslims] cannot keep an accurate count of it, so He pardoned you[7]. Recite then as much of the Qur’an as is easy for you [in the night prayers]. He knows that there are some among you who will be ill, and others traveling in the land, seeking the grace of Allah, and others fighting in Allah’s way. So recite as much of it as is easy for you; establish prayer and give zakah; and lend to Allah a goodly loan[8]. Whatever good you send forth for yourselves, you will find it with Allah, much better in condition and much greater in reward[9]. And seek forgiveness of Allah, for indeed Allah is All-Forgiving, Most-Merciful.

[7] The ruling mentioned at the beginning of this surah is lightened here. So from now on, the believers do not have to stick to any of the portions specified there; rather, they can pray whatever they can at night. It is out of the mercy of Allah upon His servants that He does not want hardship for them.
[8] i.e., giving in charity and for His causes.
[9] It will be rewarded tenfold, or 700-fold, and Allah gives even more to whoever He wills. See 2:261.

Indeed, your Lord knows, [O Muḥammad], that you stand [in prayer] almost two thirds of the night or half of it or a third of it, and [so do] a group of those with you. And Allāh determines [the extent of] the night and the day. He has known that you [Muslims] will not be able to do it[1785] and has turned to you in forgiveness, so recite what is easy [for you] of the Qur’ān. He has known that there will be among you those who are ill and others traveling throughout the land seeking [something] of the bounty of Allāh and others fighting for the cause of Allāh. So recite what is easy from it and establish prayer and give zakāh and loan Allāh a goodly loan.[1786] And whatever good you put forward for yourselves - you will find it with Allāh. It is better and greater in reward. And seek forgiveness of Allāh. Indeed, Allāh is Forgiving and Merciful.

[1785] Allāh has known that if they were to continue in such long periods of worship each night, the people would be caused much hardship.
[1786] In the form of charities and contributions to His cause.

20. Verily, your Lord knows that you do stand (to pray at night) a little less than two thirds of the night, or half the night, or a third of the night, and also a party of those with you. And Allâh measures the night and the day. He knows that you are unable to pray the whole night, so He has turned to you (in mercy). So, recite you of the Qur’ân as much as may be easy for you. He knows that there will be some among you sick, others travelling through the land, seeking of Allâh’s Bounty, yet others fighting in Allâh’s Cause. So recite as much of the Qur’ân as may be easy (for you), and perform As-Salât (Iqâmat-as-Salât ) and give Zakât, and lend to Allâh a goodly loan. And whatever good you send before you for yourselves (i.e. Nawâfil non-obligatory acts of worship: prayers, charity, fasting, Hajj and ‘Umrah), you will certainly find it with Allâh, better and greater in reward. And seek Forgiveness of Allâh. Verily, Allâh is Oft-Forgiving, Most-Merciful[4].

[4] (V.73:20) See the footnotes of (V.50:39).

Lo! thy Lord knoweth how thou keepest vigil sometimes nearly two-thirds of the night, or (sometimes) half or a third thereof, as do a party of those with thee. Allah measureth the night and the day. He knoweth that ye count it not, and turneth unto you in mercy. Recite, then, of the Qur'an that which is easy for you. He knoweth that there are sick folk among you, while others travel in the land in search of Allah's bounty, and others (still) are fighting for the cause of Allah. So recite of it that which is easy (for you), and establish worship and pay the poor-due, and (so) lend unto Allah a goodly loan. Whatsoever good ye send before you for your souls, ye will find it with Allah, better and greater in the recompense. And seek forgiveness of Allah. Lo! Allah is Forgiving, Merciful.