“The Messenger of Allah ﷺ said: ‘No prayer is acceptable in which a man does not settle his spine when bowing and when prostrating.’” (Using translation from Ibn Mājah 870)  

قَالَ رَسُولُ اللَّهِ ﷺ «لَا تُجْزِئُ صَلَاةٌ لَا يُقِيمُ الرَّجُلُ فِيهَا صُلْبَهُ فِي الرُّكُوعِ وَالسُّجُودِ»  

[Machine] The Messenger of Allah ﷺ said, "The worst of people in theft is the one who steals his own prayer." They asked, "O Messenger of Allah, how does one steal his own prayer?" He said, "He does not complete its bowing and prostration."  

قَالَ رَسُولُ اللَّهِ ﷺ «أَسْوَأُ النَّاسِ سَرِقَةً الَّذِي يَسْرِقُ صَلَاتَهُ» قَالُوا يَا رَسُولَ اللَّهِ وَكَيْفَ يَسْرِقُ صَلَاتَهُ؟ قَالَ «لَا يُتِمُّ رُكُوعَهَا وَلَا سُجُودَهَا»  

"While the Messenger of Allah ﷺ was sitting with us around him, a man came in, turned towards the Qiblah and prayed. When he had finished his prayer, he came and greeted the Messenger of Allah ﷺ and the people with Salam. The Messenger of Allah ﷺ said to him: 'And also to you. Go and pray, for you have not prayed.' So he went and prayed, and the Messenger of Allah ﷺ started watching him, and he (the man) did not know what was wrong with it. When he had finished the prayer, he came and greeted the Messenger of Allah ﷺ and the people with salam. The Messenger of Allah ﷺ said to him: 'And also to you. Go and pray, for you have not prayed.' He repeated it two or three times, then the man said: 'O Messenger of Allah, what is wrong with my prayer?' The Messenger of Allah ﷺ said: 'The prayer of any of you is not complete unless he performs wudu properly as enjoined by Allah, the Mighty and Sublime. So he should wash his face, his arms up to the elbows, and wipe his head, and (wash) his feet up to the ankles. Then he should magnify Allah (SWT) and praise Him and glorify Him.'" - (One of the narrators) Hammam said: "I heard him say: 'He should praise Allah and glorify Him and magnify Him." He said: "I heard both of them." -"He (the Prophet ﷺ) said: 'He should recite whatever is easy for him of the Quran that Allah has taught him and permitted him in it (the prayer). Then he should say the Takbir and bow until his joints settle and he is relaxed. Then he should say: 'Sami Allahu liman hamidah (Allah hears the one who praises Him)' and stand up straight until his backbone is straight (and at ease). Then he should say Takbir and prostrate until he has placed his face firmly on the ground." "I heard him say: his forehead, until his joints settle and he is relaxed. Then he should say the Takbir and sit up until his backbone is straight (and at ease). Then he should prostrate until he has placed his face firmly on the ground and he is relaxed. If he does not do that then he has not completed his prayer." (Using translation from Nasāʾī 1136)   

عَنْ عَمِّهِ رِفَاعَةَ بْنِ رَافِعٍ وَكَانَ رِفَاعَةُ وَمَالِكُ ابْنَيْ رَافِعٍ أَخَوَيْنِ مِنْ أَهْلِ بَدْرٍ قَالُوا بَيْنَمَا نَحْنُ جُلُوسٌ حَوْلَ رَسُولِ اللَّهِ ﷺ أَوْ رَسُولُ اللَّهِ ﷺ جَالِسٌ وَنَحْنُ حَوْلَهُ شَكَّ هَمَّامٌ إِذْ دَخَلَ رَجُلٌ فَاسْتَقْبَلَ الْقِبْلَةَ فَصَلَّى فَلَمَّا قَضَى الصَّلَاةَ جَاءَ فَسَلَّمَ عَلَى رَسُولِ اللَّهِ ﷺ وَعَلَى الْقَوْمِ فَقَالَ رَسُولُ اللَّهِ ﷺ «وَعَلَيْكَ ارْجِعْ فَصَلِّ فَإِنَّكَ لَمْ تُصَلِّ» فَرَجَعَ الرَّجُلُ فَصَلَّى وَجَعَلْنَا نَرْمُقُ صَلَاتَهُ لَا نَدْرِي مَا يَعِيبُ مِنْهَا فَلَمَّا قَضَى صَلَاتَهُ جَاءَ فَسَلَّمَ عَلَى رَسُولِ اللَّهِ ﷺ وَعَلَى الْقَوْمِ فَقَالَ لَهُ النَّبِيُّ ﷺ «وَعَلَيْكَ ارْجِعْ فَصَلِّ فَإِنَّكَ لَمْ تُصَلِّ» قَالَ هَمَّامٌ فَلَا أَدْرِي أَمَرَهُ بِذَلِكَ مَرَّتَيْنِ أَوْ ثَلَاثًا قَالَ الرَّجُلُ مَا أَلَوْتُ فَلَا أَدْرِي مَا عِبْتَ عَلَيَّ مِنْ صَلَاتِي فَقَالَ رَسُولُ اللَّهِ ﷺ إِنَّهَا لَا تَتِمُّ صَلَاةُ أَحَدِكُمْ حَتَّى يُسْبِغَ الْوُضُوءَ كَمَا أَمَرَهُ اللَّهُ ﷻ فَيَغْسِلُ وَجْهَهُ وَيَدَيْهِ إِلَى الْمِرْفَقَيْنِ وَيَمْسَحُ بِرَأْسِهِ وَرِجْلَيْهِ إِلَى الْكَعْبَيْنِ ثُمَّ يُكَبِّرُ اللَّهَ وَيَحْمَدُهُ ثُمَّ يَقْرَأُ مِنَ الْقُرْآنِ مَا أَذِنَ اللَّهُ ﷻ لَهُ فِيهِ ثُمَّ يُكَبِّرُ فَيَرْكَعُ فَيَضَعُ كَفَّيْهِ عَلَى رُكْبَتَيْهِ حَتَّى تَطْمَئِنَّ مَفَاصِلُهُ وَتَسْتَرْخِيَ وَيَقُولُ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ فَيَسْتَوِي قَائِمًا حَتَّى يُقِيمَ صُلْبَهُ فَيَأْخُذَ كُلُّ عَظْمٍ مَأْخَذَهُ ثُمَّ يُكَبِّرُ فَيَسْجُدُ فَيُمَكِّنُ وَجْهَهُ قَالَ هَمَّامٌ وَرُبَّمَا قَالَ جَبْهَتَهُ مِنَ الْأَرْضِ حَتَّى تَطْمَئِنَّ مَفَاصِلُهُ وَتَسْتَرْخِيَ ثُمَّ يُكَبِّرُ فَيَسْتَوِي قَاعِدًا عَلَى مَقْعَدِهِ وَيُقِيمُ صُلْبَهُ «فَوَصَفَ الصَّلَاةَ هَكَذَا أَرْبَعَ رَكَعَاتٍ حَتَّى فَرَغَ» لَا تَتِمُّ صَلَاةُ أَحَدِكُمْ حَتَّى يَفْعَلَ ذَلِكَ