I was with Uthman, and he called for ablution water and said: I heard Messenger of Allah ﷺ say: When the time for a prescribed prayer comes, if any Muslim performs ablution well and offers his prayer with humility and bowing, it will be an expiation for his past sins, so long as he has not committed a major sin; and this applies for all times. (Using translation from Muslim 228)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ مَا مِنِ امْرِئٍ مُسْلِمٍ تَحْضُرُهُ صَلَاةٌ مَكْتُوبَةٌ فَيُحْسِنُ وَضُوءَهَا وَخُشُوعَهَا وَرُكُوعَهَا إِلَّا كَانَتْ كَفَّارَةً لِمَا قَبْلَهَا مِنَ الذُّنُوبِ مَا لَمْ يُؤْتِ كَبِيرَةً وَذَلِكَ الدَّهْرَ كُلَّهُ  

One day the Messenger of Allah ﷺ led the prayer. Then turning (towards his Companions) he said: O you man, why don't you say your prayer well? Does the observer of prayer not see how he is performing the prayer, for he performs it for himself? By Allah, I see behind me as I see in front of me. (Using translation from Muslim 423)   

صَلَّى رَسُولُ اللهِ ﷺ يَوْمًا ثُمَّ انْصَرَفَ فَقَالَ يَا فُلَانُ أَلَا تُحْسِنُ صَلَاتَكَ؟ أَلَا يَنْظُرُ الْمُصَلِّي إِذَا صَلَّى كَيْفَ يُصَلِّي فَإِنَّمَا يُصَلِّي لِنَفْسِهِ إِنِّي وَاللهِ لَأُبْصِرُ مَنْ وَرَائِي كَمَا أُبْصِرُ مَنْ بَيْنِ يَدِيَّ  

[Machine] On the authority of the Prophet ﷺ , he said, "Whoever performs the prayer in the best manner in the sight of the people but corrupts it in private, then that is a form of hypocrisy by which he belittles his Lord."  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ أَحْسَنَ الصَّلَاةَ حَيْثُ يَرَاهُ النَّاسُ وَأَسَاءَهَا حَيْثُ يَخْلُو فَتِلْكَ اسْتِهَانَةٌ يَسْتَهِينُ بِهَا رَبَّهُ  

[Machine] The Prophet ﷺ went out and said, "O people, beware of showing off in secret actions." They said, "O Messenger of Allah, what is the showing off in secret actions?" He said, "When a person stands to pray and beautifies his prayer eagerly because of what he sees from the people looking at him, that is showing off in secret actions."  

خَرَجَ النَّبِيُّ ﷺ فَقَالَ أَيُّهَا النَّاسُ إِيَّاكُمْ وَشِرْكَ السَّرَائِرِ قَالُوا يَا رَسُولَ اللهِ مَا شِرْكُ السَّرَائِرِ؟ قَالَ يَقُومُ الرَّجُلُ فَيُصَلِّي فَيُزَيِّنُ صَلَاتَهُ جَاهِدًا؛ لِمَا يَرَى مِنْ نَظَرِ النَّاسِ إِلَيْهِ فَذَاكَ شِرْكُ السَّرَائِرِ  

[Machine] "He ﷺ said: Prayer is a measure, so whoever fulfills it, it is counted for him, and whoever falls short, you have known what is said regarding the unjust. And Abu Al-Husayn bin Al-Fadl Al-Qattan informed us that Abdullah bin Ja'far narrated to us, from Ya'qub bin Sufyan, from Abu Nu'aim, from Sufyan, from Abu Nasr, who is Abdullah bin Abdul Rahman, with similar wording."  

أَنَّهُ قَالَ الصَّلَاةُ مِكْيَالٌ فَمَنْ وَفَّى أُوفِيَ لَهُ وَمَنْ نَقَصَ فَقَدْ عَلِمْتُمْ مَا قِيلَ لِلْمُطَفِّفِينَ 3587 وَأَخْبَرَنَا أَبُو الْحُسَيْنِ بْنُ الْفَضْلِ الْقَطَّانُ أنبأ عَبْدُ اللهِ بْنُ جَعْفَرٍ ثنا يَعْقُوبُ بْنُ سُفْيَانَ ثنا أَبُو نُعَيْمٍ ثنا سُفْيَانُ عَنْ أَبِي نَصْرٍ وَهُوَ عَبْدُ اللهِ بْنُ عَبْدِ الرَّحْمَنِ بِمَعْنَاهُ