Mishkat al-Masabih 1235
‘Uthman b. Abul ‘As said he heard God’s Messenger say:
David had an hour during the night in which he would waken his family and say, “Family of David, get up and pray, for this is an hour in which God who is great and glorious answers petitions, except to a magician or a tax-gatherer.” 

Ahmad transmitted it.
وَعَنْ عُثْمَانَ بْنِ أَبِي الْعَاصِ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم يَقُول: 
" كَانَ لِدَاوُدَ عَلَيْهِ السَّلَامُ مِنَ اللَّيْلِ سَاعَةٌ يُوقِظُ فِيهَا أَهْلَهُ يَقُولُ: يَا آلَ دَاوُدَ قُومُوا فَصَلُّوا فَإِنَّ هَذِهِ سَاعَةٌ يَسْتَجِيبُ اللَّهُ عَزَّ وَجَلَّ فِيهَا الدُّعَاءَ إِلَّا لِسَاحِرٍ أَوْ عشار ". رَوَاهُ أَحْمد