Sahih Muslim
Sahih Muslim 756 a
The best prayer is that in which one stands for a long time (tuwlul-qunut)
Arabic hadith text
حَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، أَخْبَرَنَا أَبُو عَاصِمٍ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، أَخْبَرَنِي أَبُو الزُّبَيْرِ، عَنْ جَابِرٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم "أَفْضَلُ الصَّلاَةِ طُولُ الْقُنُوتِ "
Translation
Jabir reported Allah's Messenger (ﷺ) as saying
The most excellent prayer is that in which the duration of standing is longer.