Sunan an-Nasa'i, Volume 2, Book 12, Hadith 1073 (DarusSalam) ⓘ

It was narrated that Ibn Sirin said: "Some of those who prayed the Subh prayer with the Messenger of Allah narrated to me that when he said: Sami'Allahu liman hamidah (Allah hears those who praise Him)' in the second rak'ah, he stood for a while."

أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا بِشْرُ بْنُ الْمُفَضَّلِ، عَنْ يُونُسَ، عَنِ ابْنِ سِيرِينَ، قَالَ حَدَّثَنِي بَعْضُ، مَنْ صَلَّى مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم صَلاَةَ الصُّبْحِ فَلَمَّا قَالَ ‏ "‏ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ ‏" ‏ ‏.‏ فِي الرَّكْعَةِ الثَّانِيَةِ قَامَ هُنَيْهَةً ‏.‏