Sunan an-Nasa'i, Volume 2, Book 12, Hadith 1150 (DarusSalam) ⓘ
It was narrated that Abdullah said: "The Messenger of Allah used to say the takbir every time he got up, went down, stood and sat. Abu Bakr, 'Umar, and 'Uthman (did likewise)."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ أَبِي إِسْحَاقَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ الأَسْوَدِ، عَنِ الأَسْوَدِ، وَعَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يُكَبِّرُ فِي كُلِّ رَفْعٍ وَوَضْعٍ وَقِيَامٍ وَقُعُودٍ وَأَبُو بَكْرٍ وَعُمَرُ وَعُثْمَانُ رضى الله عنهم .
also referenced under: Hadith 1149 (Reference) & Book 12, Hadith 121 (In-Book)