bow till you feel at ease
sit with calmness till you feel at ease (do not hurry)
until his joints settle and he is relaxed
until he has placed his face firmly on
the ground and he is relaxed
The narrations of the Hadith clarify the issue: calming, settling, relaxing, and feeling at ease. In short: "الطمأنينة". (Thanks to @Hicham LEMGHARI).
The first two quoted statements above are from the narration in Sahih al-Bukhari, while the latter two are from the narration in Sunan an-Nasa'i, which is quoted below:
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ يَزِيدَ الْمُقْرِئُ
أَبُو يَحْيَى، بِمَكَّةَ - وَهُوَ بَصْرِيٌّ - قَالَ حَدَّثَنَا أَبِي
قَالَ، حَدَّثَنَا هَمَّامٌ، قَالَ حَدَّثَنَا إِسْحَاقُ بْنُ عَبْدِ
اللَّهِ بْنِ أَبِي طَلْحَةَ، أَنَّ عَلِيَّ بْنَ يَحْيَى بْنِ خَلاَّدِ
بْنِ مَالِكِ بْنِ رَافِعِ بْنِ مَالِكٍ، حَدَّثَهُ عَنْ أَبِيهِ، عَنْ
عَمِّهِ، رِفَاعَةَ بْنِ رَافِعٍ قَالَ بَيْنَمَا رَسُولُ اللَّهِ صلى
الله عليه وسلم جَالِسٌ وَنَحْنُ حَوْلَهُ إِذْ دَخَلَ رَجُلٌ فَأَتَى
الْقِبْلَةَ فَصَلَّى فَلَمَّا قَضَى صَلاَتَهُ جَاءَ فَسَلَّمَ عَلَى
رَسُولِ اللَّهِ صلى الله عليه وسلم وَعَلَى الْقَوْمِ فَقَالَ لَهُ
رَسُولُ اللَّهِ صلى الله عليه وسلم " وَعَلَيْكَ اذْهَبْ فَصَلِّ
فَإِنَّكَ لَمْ تُصَلِّ " . فَذَهَبَ فَصَلَّى فَجَعَلَ رَسُولُ
اللَّهِ صلى الله عليه وسلم يَرْمُقُ صَلاَتَهُ وَلاَ يَدْرِي مَا
يَعِيبُ مِنْهَا فَلَمَّا قَضَى صَلاَتَهُ جَاءَ فَسَلَّمَ عَلَى رَسُولِ
اللَّهِ صلى الله عليه وسلم وَعَلَى الْقَوْمِ فَقَالَ لَهُ رَسُولُ
اللَّهِ صلى الله عليه وسلم " وَعَلَيْكَ اذْهَبْ فَصَلِّ فَإِنَّكَ
لَمْ تُصَلِّ " . فَأَعَادَهَا مَرَّتَيْنِ أَوْ ثَلاَثًا فَقَالَ
الرَّجُلُ يَا رَسُولَ اللَّهِ مَا عِبْتَ مِنْ صَلاَتِي فَقَالَ رَسُولُ
اللَّهِ صلى الله عليه وسلم " إِنَّهَا لَمْ تَتِمَّ صَلاَةُ
أَحَدِكُمْ حَتَّى يُسْبِغَ الْوُضُوءَ كَمَا أَمَرَهُ اللَّهُ عَزَّ
وَجَلَّ فَيَغْسِلَ وَجْهَهُ وَيَدَيْهِ إِلَى الْمِرْفَقَيْنِ
وَيَمْسَحَ بِرَأْسِهِ وَرِجْلَيْهِ إِلَى الْكَعْبَيْنِ ثُمَّ يُكَبِّرَ
اللَّهَ عَزَّ وَجَلَّ وَيَحْمَدَهُ وَيُمَجِّدَهُ " . قَالَ
هَمَّامٌ وَسَمِعْتُهُ يَقُولُ " وَيَحْمَدَ اللَّهَ وَيُمَجِّدَهُ
وَيُكَبِّرَهُ " . قَالَ فَكِلاَهُمَا قَدْ سَمِعْتُهُ يَقُولُ قَالَ
" وَيَقْرَأَ مَا تَيَسَّرَ مِنَ الْقُرْآنِ مِمَّا عَلَّمَهُ اللَّهُ
وَأَذِنَ لَهُ فِيهِ ثُمَّ يُكَبِّرَ وَيَرْكَعَ حَتَّى تَطْمَئِنَّ
مَفَاصِلُهُ وَتَسْتَرْخِيَ ثُمَّ يَقُولَ سَمِعَ اللَّهُ لِمَنْ
حَمِدَهُ ثُمَّ يَسْتَوِيَ قَائِمًا حَتَّى يُقِيمَ صُلْبَهُ ثُمَّ
يُكَبِّرَ وَيَسْجُدَ حَتَّى يُمَكِّنَ وَجْهَهُ " . وَقَدْ
سَمِعْتُهُ يَقُولُ " جَبْهَتَهُ حَتَّى تَطْمَئِنَّ مَفَاصِلُهُ
وَتَسْتَرْخِيَ وَيُكَبِّرَ فَيَرْفَعَ حَتَّى يَسْتَوِيَ قَاعِدًا عَلَى
مَقْعَدَتِهِ وَيُقِيمَ صُلْبَهُ ثُمَّ يُكَبِّرَ فَيَسْجُدَ حَتَّى
يُمَكِّنَ وَجْهَهُ وَيَسْتَرْخِيَ فَإِذَا لَمْ يَفْعَلْ هَكَذَا لَمْ
تَتِمَّ صَلاَتُهُ " .
It was narrated that Rifa'ah bin Rafi' said: "While the Messenger of
Allah () 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 () and the people with Salam. The
Messenger of Allah () 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 () 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 () and the people with salam. The Messenger of
Allah () 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 () 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
()) 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." (Sahih)