A man entered the mosque while Messenger of Allah ﷺ was sitting in one side of the mosque. The man prayed, came, and greeted the Prophet. Messenger of Allah ﷺ said to him, "Wa 'Alaikas Salam (returned his greeting). Go back and pray as you have not prayed (properly)." The man returned, repeated his prayer, came back and greeted the Prophet. The Prophet ﷺ said, "Wa alaika-s-Salam (returned his greeting). Go back and pray again as you have not prayed (properly)." The man said at the second or third time, "O Messenger of Allah ﷺ! Kindly teach me how to pray". The Prophet ﷺ said, "When you stand for prayer, perform ablution properly and then face the Qibla and say Takbir (Allahu-Akbar), and then recite what you know from the Qur'an, and then bow with calmness till you feel at ease then rise from bowing, till you stand straight, and then prostrate calmly (and remain in prostration) till you feel at ease, and then raise (your head) and sit with calmness till you feel at ease and then prostrate with calmness (and remain in prostration) till you feel at ease, and then raise (your head) and sit with calmness till you feel at ease in the sitting position, and do likewise in whole of your prayer." And Abu Usama added, "Till you stand straight." (See Hadith No. 759, Vol.1) (Using translation from Bukhārī 6251)   

أَنَّ رَجُلًا دَخَلَ الْمَسْجِدَ وَرَسُولُ اللهِ ﷺ جَالِسٌ فِي نَاحِيَةِ الْمَسْجِدِ فَصَلَّى ثُمَّ جَاءَ فَسَلَّمَ عَلَيْهِ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ وَعَلَيْكَ السَّلَامُ ارْجِعْ فَصَلِّ فَإِنَّكَ لَمْ تُصَلِّ فَرَجَعَ فَصَلَّى ثُمَّ جَاءَ فَسَلَّمَ فَقَالَ وَعَلَيْكَ السَّلَامُ ارْجِعْ فَصَلِّ فَإِنَّكَ لَمْ تُصَلِّ فَقَالَ فِي الثَّالِثَةِ أَوْ فِي الَّتِي بَعْدَهَا عَلِّمْنِي يَا رَسُولَ اللهِ فَقَالَ إِذَا قُمْتَ إِلَى الصَّلَاةِ فَأَسْبِغِ الْوُضُوءَ ثُمَّ اسْتَقْبِلِ الْقِبْلَةَ فَكَبِّرْ ثُمَّ اقْرَأْ بِمَا تَيَسَّرَ مَعَكَ مِنَ الْقُرْآنِ ثُمَّ ارْكَعْ حَتَّى تَطْمَئِنَّ رَاكِعًا ثُمَّ ارْفَعْ حَتَّى تَسْتَوِيَ قَائِمًا ثُمَّ اسْجُدْ حَتَّى تَطْمَئِنَّ سَاجِدًا ثُمَّ ارْفَعْ حَتَّى تَطْمَئِنَّ جَالِسًا ثُمَّ افْعَلْ ذَلِكَ فِي صَلَاتِكَ كُلِّهَا  

[Machine] The Messenger of Allah, ﷺ , used to start the prayer with takbeer and mention the hadith.  

كَانَ رَسُولُ اللهِ ﷺ يَفْتَتِحُ الصَّلَاةَ بِالتَّكْبِيرِ وَذَكَرَ الْحَدِيثَ  

[Machine] The Messenger of Allah, ﷺ , used to begin the prayer with the takbeer (saying Allahu Akbar) and recite "Alhamdulillahi Rabbil 'Aalameen" (Praise be to Allah, the Lord of all the worlds) [Surah Al-Fatiha, verse 2].  

رَسُولَ اللهِ ﷺ كَانَ يَفْتَتِحُ الصَّلَاةَ بِالتَّكْبِيرِ وَالْقِرَاءَةِ بِ {الْحَمْدُ لِلَّهِ رَبِّ الْعَالَمِينَ} [الفاتحة 2]  

[Machine] Narrated by Ali, he said that the Prophet ﷺ said, "The key to prayer is purification, the initiation of prayer is the takbeer (saying Allahu Akbar), and the conclusion of prayer is the tasleem (saying salaam)." Imam Shafi'i (may Allah have mercy on him) said this was also narrated from Ibn Mas'ood.  

عَنْ عَلِيٍّ رَفَعَهُ إِلَى النَّبِيِّ ﷺ قَالَ مِفْتَاحُ الصَّلَاةِ الطَّهُورُ وَإِحْرَامُهَا التَّكْبِيرُ وَإِحْلَالُهَا التَّسْلِيمُ قَالَ الشَّافِعِيُّ رَحْمَةُ اللهِ عَلَيْهِ فِي الْقَدِيمِ وَكَذَلِكَ رُوِيَ عَنِ ابْنِ مَسْعُودٍ  

The Messenger of Allah ﷺ said: “The key to prayer is purification; entering it is takbeer and exiting it is tasleem.” (Using translation from Aḥmad 1006)   

مِفْتَاحُ الصَّلَاةِ الطَّهُورُ وَإِحْرَامُهَا التَّكْبِيرُ وَانْقِضَاؤُهَا التَّسْلِيمُ