We did not know what we should say when we sat during prayer. The Messenger of Allah ﷺ was taught (by Allah). He then narrated the tradition to the same effect. Sharik reported from Jami', from AbuWa'il on the authority of Abdullah ibn Mas'ud something similar. He said: He used to teach us also some other words, but he did not teach them as he taught us the tashahhud: O Allah, join our hearts, mend our social relationship, guide us to the path of peace, bring us from darkness to light, save us from obscenities, outward or inward, and bless our ears, our eyes, our hearts, our wives, our children, and relent toward us; Thou art the Relenting, the Merciful. And make us grateful for Thy blessing and make us praise it while accepting it and give it to us in full. (Using translation from Abū Dāʾūd 969)   

كُنَّا لَا نَدْرِي مَا نَقُولُ إِذَا جَلَسْنَا فِي الصَّلَاةِ وَكَانَ رَسُولُ اللَّهِ ﷺ قَدْ عَلِمَ جَوَامِعَ الْكَلِمِ وَخَوَاتِمَهُ قَالَ فَذَكَرَ التَّشَهُّدَ وَقَالَ كَانَ رَسُولُ اللَّهِ ﷺ يُعَلِّمُنَا كَلِمَاتٍ كَمَا يُعَلِّمُنَا التَّشَهُّدَ «اللَّهُمَّ أَلَّفْ بَيْنَ قُلُوبِنَا وَأَصْلِحْ ذَاتَ بَيْنِنَا وَاهْدِنَا سُبُلَ السَّلَامِ وَنَجِّنَا مِنَ الظُّلُمَاتِ إِلَى النُّورِ وَجَنِّبْنَا الْفَوَاحِشَ مَا ظَهَرَ مِنْهَا وَمَا بَطَنَ وَبَارِكْ لَنَا فِي أَسْمَاعِنَا وَأَبْصَارِنَا وَقُلُوبِنَا وَأَزْوَاجِنَا وَذُرِّيَّاتِنَا وَتُبْ عَلَيْنَا إِنَّكَ أَنْتَ التَّوَّابُ الرَّحِيمُ وَاجْعَلْنَا شَاكِرِينَ لِنِعَمِكَ مُثْنِينَ بِهَا عَلَيْكَ قَابِلِينَ لَهَا وَأَتِمَّهَا عَلَيْنَا»  

[Machine] The Prophet ﷺ used to teach us the Tashahhud in prayer, just as he used to teach us a chapter from the Quran. He would teach us things that he had not taught us before, just as he taught us the Tashahhud. "O Allah, unite our hearts, reconcile between us, guide us on the path of peace, and save us from darkness into light. Keep us protected in our hearing, sight, and spouses, and make us grateful for Your blessings, praising and accepting them. Complete Your blessings upon us."  

كَانَ نَبِيُّ اللَّهِ ﷺ يُعَلِّمُنَا التَّشَهُّدَ فِي الصَّلَاةِ كَمَا يُعَلِّمُنَا السُّورَةَ مِنَ الْقُرْآنِ وَيُعَلِّمُنَا مَا لَمْ يَكُنْ يُعَلِّمُنَا كَمَا يُعَلِّمُنَا التَّشَهُّدَ «اللَّهُمَّ أَلِّفْ بَيْنَ قُلُوبِنَا وَأَصْلِحْ ذَاتَ بَيْنِنَا وَاهْدِنَا سُبُلَ السَّلَامِ وَنَجِّنَا مِنَ الظُّلُمَاتِ إِلَى النُّورِ وَجَنِّبْنَا الْفَوَاحِشَ مَا ظَهْرَ مِنْهَا وَمَا بَطْنَ اللَّهُمَّ احْفَظْنَا فِي أَسْمَاعِنَا وَأَبْصَارِنَا وَأَزْوَاجِنَا وَاجْعَلْنَا شَاكِرِينَ لِنِعْمَتِكَ مُثْنِينَ بِهَا عَلَيْكَ قَابِلِينَ بِهَا فَأَتْمِمْهَا عَلَيْنَا»  

[Machine] The Messenger of Allah ﷺ used to teach us the following words: "O Allah, reconcile our hearts, unite us, guide us on the path of peace, save us from darkness and guide us towards light, and keep us away from indecency, both apparent and hidden. O Allah, bless our hearing, our sight, our hearts, our spouses, our children, and turn to us in forgiveness. Indeed, You are the Accepter of repentance, the Merciful. Make us grateful for Your blessings and allow us to praise You and complete them for us."  

كَانَ رَسُولُ اللهِ ﷺ يُعَلِّمُنَا هَذَا الْكَلَامَ «اللهُمَّ أَصْلِحْ ذَاتَ بَيْنِنَا وَأَلِّفْ بَيْنَ قُلُوبِنَا وَاهْدِنَا سُبُلَ السَّلَامِ وَنَجِّنَا مِنَ الظُّلُمَاتِ إِلَى النُّورِ وَجَنِّبْنَا الْفَوَاحِشَ مَا ظَهَرَ لَنَا وَمَا بَطَنَ اللهُمَّ بَارِكْ لَنَا فِي أَسْمَاعِنَا وَأَبْصَارِنَا وَقُلُوبِنَا وَأَزْوَاجِنَا وَذُرِّيَّاتِنَا وَتُبْ عَلَيْنَا؛ إِنَّكَ أَنْتَ التَّوَّابُ الرَّحِيمُ وَاجْعَلْنَا شَاكِرِينَ لِنِعْمَتِكَ مُثْنِينَ بِهَا قَائِلِيهَا وَأَتِمَّهَا عَلَيْنَا»  

"اللَّهُمَّ أَصْلِحْ ذَاتَ بَينِنِا، وَألِّفْ بَينَ قُلُوبِنَا، وَاهْدِنَا سُبُلَ السَّلام، وَنَجِّنَا مِنَ الظلُمَاتِ إِلَى النُّورِ، وَجنِّبْنَا الْفَوَاحِشَ مَا ظَهَرَ مِنْهَا وَمَا بَطَنَ، اللَّهُمَّ بَارِكَ لَنَا في أسْماعنَا وَأبْصَارِنَا وَقُلوبنَا وَأروَاحِنَا وَذَرَارِينَا، وَتُبْ عَلَينَا إِنَّكَ أنت التوَّابُ الرَّحِيمُ، وَاجْعَلنَا شَاكِرِينَ لِنِعْمَتِكَ، مُثْنِينَ بِهَا قَابِلِينَ لَهَا وَأَتِمَّهَا عَلَينَا".