Hadith Q578

وَأَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّمَا كَانَ يُكَبِّرُ فِي بَعْضِ الرَّفْعِ لَا فِي كُلِّهَا، لَمْ يُكَبِّرِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عِنْدَ رَفْعِهِ رَأْسَهُ عَنِ الرُّكُوعِ، وَإِنَّمَا كَانَ يُكَبِّرُ فِي كُلِّ رَفْعٍ خَلَا عِنْدَ رَفْعِهِ رَأْسَهُ مِنَ الرُّكُوعِ‏.‏
The Prophet ﷺ did not say "Allahu Akbar" every time he stood up, but sometimes he would say it. When he ﷺ raised his head from bowing (ruku'), he would say "Allahu Akbar," but except for raising his head from bowing, he ﷺ would say "Allahu Akbar" every time he stood up.
Hadith Reference صحيح ابن خزيمه / جماع أبواب الأذان والإقامة / Q578