Mishkat al-Masabih 4 Prayer كتاب الصلاة 294

وَعَنْ أَنَسٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا قَالَ: «سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ» قَامَ حَتَّى نَقُولَ: قَدْ أَوْهَمَ ثُمَّ يَسْجُدُ وَيَقْعُدُ بَيْنَ السَّجْدَتَيْنِ حَتَّى نَقُولَ: قَدْ أوهم. رَوَاهُ مُسلم

Anas said: When the Prophet said, “God listens to him who praises Him,” he stood so long that we thought he had omitted something; then he would prostrate himself and sit between the sajdas so long that we thought he had omitted something. Muslim transmitted it.