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[1].
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(V.73:20) See the footnotes of (V.50:39).