It is narrated from Ibn Abbas (may Allah be pleased with them both) that the Prophet (ﷺ) was commanded to prostrate on seven parts. Among them, he also mentioned both his palms and both his knees.
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 242
Hadith Takhrijأخرجه البخارى: الأذان، باب السجود على سبعة اعظم: 809، 810 ، 815- ومسلم، الصلاة، باب أعضاء السجود والنهي عن كف الشعر والثوب وعقص الرأس في الصلاة 490۔