Sahih Bukhari Volume 9, Book 91, Hadith 7033

فَزَعَمَتْ حَفْصَةُ أَنَّهَا قَصَّتْهَا عَلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏"‏ إِنَّ عَبْدَ اللَّهِ رَجُلٌ صَالِحٌ لَوْ كَانَ يُكْثِرُ الصَّلاَةَ مِنَ اللَّيْلِ ‏"‏‏.‏ قَالَ الزُّهْرِيُّ وَكَانَ عَبْدُ اللَّهِ بَعْدَ ذَلِكَ يُكْثِرُ الصَّلاَةَ مِنَ اللَّيْلِ‏.

Hafsa told me that she had mentioned it to the Prophet and he said, "'Abdullah is a righteous man if he only prays more at night." (Az-Zuhri said, "After that, 'Abdullah used to pray more at night.")