Ibn ‘Abbās (may Allah be pleased with him and his father) reported that the Prophet (may Allah's peace and blessings be upon him) said:
"I have been commanded to prostrate on seven bones: the forehead (and he pointed to his nose), the hands, the knees, and the extremities of the feet, and not to tuck up the clothes and hair."
Reported by Al-Bukhari (No. 812, 809, 816), Muslim (No. 490b, 490d, 490e), Abu Dawud (No. 889), An-Nasa’i (No. 1096, 1097, 1113), Ibn Majah (No. 883, 884), Ahmad (No. 1839, 2186, 2310, 2396, 2453, 2457, 2459, 2465) and Ad-Darimi (No. 1284, 1285).
The Prophet (may Allah's peace and blessings be upon him) clarified that Allah commanded him to prostrate in prayer on seven body parts, which are:
First: The forehead, i.e., the upper part of the face above the nose and eyes. The Prophet (may Allah's peace and blessings be upon him) pointed with his hand to his nose to clarify that the forehead and the nose represent one part of the seven and to stress the fact that one must touch the ground with his nose in prostration.
The second and third parts: The two hands.
The fourth and fifth: The knees.
The sixth and seventh: The toes of both feet.
He commanded us not to tie our hair or fold up our clothes when prostrating on the ground to protect them; rather, we should let them spread out and fall on the ground to prostrate along with the body parts.
Lessons
It is a must in prayer to prostrate on the seven parts.
It is disliked to tuck up and fold back the clothes and hair in prayer.
The one praying must maintain his composure during his prayer by placing the seven parts included in Sujūd (prostration) on the ground and resting on them until he recites the prescribed Dhikr (remembrance of Allah).
The prohibition of folding back the hair is exclusively prescribed for men apart from women, who are commanded to cover themselves in prayer.
Explanation in Arabic
بَيَّنَ النبيُّ صلى الله عليه وسلم بأنَّ اللهَ أَمَرَه عند الصلاة أنْ يَسجُدَ على سبعةٍ من أعضاء الجسم؛ وهي:
أولاً: الجبهة: وهي: صفحة الوجه فوق الأنف والعينين،
وأشار صلى الله عليه وسلم بيده إلى أنفِه، مُبَيِّنًا أن الجَبْهةَ والأنف عضو واحد من السبعة، وتأكيدًا على أنَّ الساجِد يُلامِسُ بأنفِه الأرضَ.
العضو الثاني والثالث: اليدان.
الرابع والخامس: الرُّكْبتان.
السادس والسابع: أصابع القدمين.
وأَمَرَنا أنْ لا نَربِطَ شعورنًا، أو نَجمعَ ثيابَنا بعضَها على بعض عند السجود على الأرض صيانةً لها؛ بل نُرسِلُها حتى تقع على الأرض، فتسجد مع الأعضاء.
وجوب السُّجود في الصلاة على الأعَضاء السَّبعة.
كراهية جَمْعِ وضَمِّ الثَّوب والشَّعَر في الصلاة.
يجب على المصلي أن يطمئن في صلاته، وذلك بأنْ يضع أعضاء السجود السبعة على الأرض، ويستقر عليها حتى يأتي بالذكر المشروع.
النهيُ عن كَفِّ الشَّعَرِ خاصٌّ بالرجال دون النساء؛ لأن المرأة في الصلاة مأمورة بالتستر.