“Our Lord, the Blessed and Exalted, descends when one third of the night remains, every night and He says: ‘Who will ask of Me, that I may give him? Who will call upon Me, that I may answer him? Who will ask My forgiveness, that I may forgive him?’ until dawn comes.” Hence they used to prefer voluntary prayers at the end of the night rather than at the beginning.
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ يَنْزِلُ رَبُّنَا تَبَارَكَ وَتَعَالَى حِينَ يَبْقَى ثُلُثُ اللَّيْلِ الآخِرُ كُلَّ لَيْلَةٍ فَيَقُولُ مَنْ يَسْأَلُنِي فَأُعْطِيَهُ؟ مَنْ يَدْعُونِي فَأَسْتَجِيبَ لَهُ؟ مَنْ يَسْتَغْفِرُنِي فَأَغْفِرَ لَهُ؟ حَتَّى يَطْلُعَ الْفَجْرُ فَلِذَلِكَ كَانُوا يَسْتَحِبُّونَ صَلاَةَ آخِرِ اللَّيْلِ عَلَى أَوَّلِهِ