Inna rabbaka ya'lamu annaka taqumu adna min thuluthayi al-layli wa nisfahu wa thuluthahu wa ta'ifatun min alladhina ma'aka wa Allahu yuqaddiru al-layla wa an-nahara alima an lan tuhsuhu fa taba alaykum fa iqrau maa tayassara min al-qur'ani alima an sayakunu min kum marda wa akharuna yadribuna fi al-ardi yabtaghuna min fadli Allahi wa akharuna yuqatiluna fi sabili Allahi fa iqrau maa tayassara min hu wa aqimu as-salata wa atu az-zakata wa aqridu Allaha qardan hasanan wa maa tuqaddimu li anfusikum min khayrin tajiduhu inda Allahi huwa khayran wa athama ajran wa istaghfiru Allaha inna Allaha ghafurun rahimun
Surely, your Lord knows that you stand 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 Allah measures the night and the day. He knows that you are unable to pray the whole night, so He has turned to you. So, recite you of the Quran as much as may be easy for you. He knows that there will be some among you sick, others traveling through the land, seeking of Allah's bounty, yet others fighting in Allah's cause. So recite as much of the Quran as may be easy and perform salat and give zakat and lend to Allah a handsome loan. And whatever good you send before you for yourselves, you will certainly find it with Allah, better and greater in reward And seek forgiveness of Allah. Surely, Allah is Oft-Forgiving, Most-Merciful
The following is an excerpt of commentary on this ayah, from Tafsir Ibn Kathir:
Sometimes like this and sometimes like that, and all of these are done unintentionally. However, you all are not able to be consistent with the night prayer Allah has commanded you, because it is difficult for you... sometimes the night and day are equal, and sometimes one of them will be longer or shorter than the other... stand and pray during the night as much as is easy... He knows that there will be people of this nation who will have excuses for not praying the (voluntary) night prayer. They are those who are ill and therefore they are not able to perform it, and those who are traveling in the land seeking the bounty of Allah in business and trade, and others who will be busy with that which is more important to them. An example of this is going on expeditions to fight in the way of Allah. This Ayah, rather, this entire Surah was revealed in Makkah even though fighting was not legislated until after it was revealed. Thus, it is among the greatest of the signs of prophethood, because it informs about unseen matters of the future... establish your obligatory prayers and pay your obligatory Zakah. This is a proof for those who say that Zakah was made obligatory in Makkah, but the various amounts of Nisab and how much was to be given was clarified in Al-Madinah. And Allah knows best... lend to Allah from charitable donations. For verily, Allah will reward for this the best and most abundant of rewards... for all that you send before yourselves, you will get it (back) and it will be better than what you kept for yourselves in the worldly life... remember Him and seek forgiveness from Him often for all of your matters. For verily, He is Most Forgiving, Most Merciful to whoever seeks His forgiveness
A Quranic Journal: Surah al-Muzzammil ayah 20