Quran 73:20

إِنَّ رَبَّكَ يَعۡلَمُ أَنَّكَ تَقُومُ أَدۡنَىٰ مِن ثُلُثَىِ ٱلَّيۡلِ وَنِصۡفَهُ ۥ وَثُلُثَهُ ۥ وَطَآٮِٕفَةٌ۬ مِّنَ ٱلَّذِينَ مَعَكَ‌ۚ وَٱللَّهُ يُقَدِّرُ ٱلَّيۡلَ وَٱلنَّہَارَ‌ۚ عَلِمَ أَن لَّن تُحۡصُوهُ فَتَابَ عَلَيۡكُمۡ‌ۖ فَٱقۡرَءُواْ مَا تَيَسَّرَ مِنَ ٱلۡقُرۡءَانِ‌ۚ عَلِمَ أَن سَيَكُونُ مِنكُم مَّرۡضَىٰ‌ۙ وَءَاخَرُونَ يَضۡرِبُونَ فِى ٱلۡأَرۡضِ يَبۡتَغُونَ مِن فَضۡلِ ٱللهِ‌ۙ وَءَاخَرُونَ يُقَـٰتِلُونَ فِى سَبِيلِ ٱللهِ‌ۖ فَٱقۡرَءُواْ مَا تَيَسَّرَ مِنۡهُ‌ۚ وَأَقِيمُواْ ٱلصَّلَوٰةَ وَءَاتُواْ ٱلزَّكَوٰةَ وَأَقۡرِضُواْ ٱللَّهَ قَرۡضًا حَسَنً۬ا‌ۚ وَمَا تُقَدِّمُواْ لِأَنفُسِكُم مِّنۡ خَيۡرٍ تَجِدُوهُ عِندَ ٱللهِ هُوَ خَيۡرً۬ا وَأَعۡظَمَ أَجۡرً۬ا‌ۚ وَٱسۡتَغۡفِرُواْ ٱللَّهَ‌ۖ إِنَّ ٱللَّهَ غَفُورٌ۬ رَّحِيمُۢ ٢٠

Your Lord knows that you meditate during two-thirds of the night, or half of it, or one-third of it, and so do some of those who believed with you. ALLAH has designed the night and the day, and He knows that you cannot always do this. He has pardoned you. Instead, you shall read what you can of the Quran. He knows that some of you may be ill, others may be traveling on Earth, in pursuit of ALLAH’s provisions, and others may be striving in the cause of ALLAH. You shall read what you can of it, and observe the Salat (Contact Prayers), give the Zakat (Obligatory Charity), and lend ALLAH a loan of righteousness. Whatever good you send ahead on behalf of your souls, you will find it at ALLAH far better and generously rewarded. And implore ALLAH for forgiveness. ALLAH is Forgiver, Most Merciful.