عَنْ أَبِي الْأَحْوَصِ عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ قَالَ: إِنَّ مُحَمَّدًا عُلِّمَ فَوَاتِحَ الْخَيْرِ وَجَوَامِعَهُ وَخَوَاتِمَهُ (زَادَ فِي رِوَايَةٍ: وَإِنَّا كُنَّا لَا نَدْرِي مَا نَقُولُهُ فِي صَلَاتِنَا حَتَّى عَلَّمَنَا) فَقَالَ: ((إِذَا قَعَدْتُّمْ فِي كُلِّ رَكْعَتَيْنِ فَقُولُوا: التَّحِيَّاتُ لِلَّهِ (فَذَكَرَ مِثْلَ مَا تَقَدَّمَ إِلَى قَوْلِهِ عَبْدُهُ وَرَسُولُهُ) قَالَ ثُمَّ لِيَتَخَيَّرْ أَحَدُكُمْ مِنَ الدُّعَاءِ أَعْجَبَهُ إِلَيْهِ فَلْيَدْعُ رَبَّهُ عَزَّ وَجَلَّ))
Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: Indeed, Muhammad (peace and blessings be upon him) was taught the initial, comprehensive, and concluding matters of goodness and virtue, while we did not know what to say in prayer (Tashahhud). He (peace and blessings be upon him) taught us this and said: When you sit after two rak'ahs, recite: "At-tahiyyatu lillah... ‘abduhu wa rasuluhu." Then each of you should choose any supplication he likes and call upon his Lord with it.