بُلُوغُ الْمَرَامِ
Bulugh al-Maram 311
The Book of Prayer
{ رَأَيْتُ رَسُولَ اَللَّهِ - صلى الله عليه وسلم -إِذَا سَجَدَ وَضَعَ رُكْبَتَيْهِ قَبْلَ يَدَيْهِ } أَخْرَجَهُ اَلْأَرْبَعَةُ . [1]
I saw the Prophet (ﷺ) placing his knees (on the ground) before his hands when he prostrated. [Reported by al-Arba'ah].
Sunnah.com reference: Book 2, Hadith 198