Sunan an-Nasa'i 1179
It was narrated that 'Abdur-Rahman bin Al-Asamm said:
"Anas bin Malik was asked about the takbir in the prayer. He said: "The takbir should be said when bowing, when prostrating, when raising one's head from prostration and when standing up following the first two rak'ahs.' Hutaim said: 'From whom did you learn this?' He said: 'From the Prophet (ﷺ), Abu Bakr and 'Umar, may Allah (SWT) be pleased with them.' Then he fell silent and Hutaim said to him: 'And 'Uthman?' He said: 'And 'Uthman.'"
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَصَمِّ، قَالَ سُئِلَ أَنَسُ بْنُ مَالِكٍ عَنِ التَّكْبِيرِ، فِي الصَّلاَةِ فَقَالَ يُكَبِّرُ إِذَا رَكَعَ وَإِذَا سَجَدَ وَإِذَا رَفَعَ رَأْسَهُ مِنَ السُّجُودِ وَإِذَا قَامَ مِنَ الرَّكْعَتَيْنِ ‏.‏ فَقَالَ حُطَيْمٌ عَمَّنْ تَحْفَظُ هَذَا فَقَالَ عَنِ النَّبِيِّ صلى الله عليه وسلم وَأَبِي بَكْرٍ وَعُمَرَ - رضى الله عنهما - ثُمَّ سَكَتَ ‏.‏ فَقَالَ لَهُ حُطَيْمٌ وَعُثْمَانُ قَالَ وَعُثْمَانُ ‏.‏