Sunan an-Nasai Book 12, Hadith 1102

أَخْبَرَنِي أَحْمَدُ بْنُ نَاصِحٍ، قَالَ حَدَّثَنَا ابْنُ إِدْرِيسَ، قَالَ سَمِعْتُ عَاصِمَ بْنَ كُلَيْبٍ، يَذْكُرُ عَنْ أَبِيهِ، عَنْ وَائِلِ بْنِ حُجْرٍ، قَالَ قَدِمْتُ الْمَدِينَةَ فَقُلْتُ لأَنْظُرَنَّ إِلَى صَلاَةِ رَسُولِ اللَّهِ صلى الله عليه وسلم فَكَبَّرَ وَرَفَعَ يَدَيْهِ حَتَّى رَأَيْتُ إِبْهَامَيْهِ قَرِيبًا مِنْ أُذُنَيْهِ فَلَمَّا أَرَادَ أَنْ يَرْكَعَ كَبَّرَ وَرَفَعَ يَدَيْهِ ثُمَّ رَفَعَ رَأْسَهُ فَقَالَ ‏ "‏ سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ ‏"‏ ‏.‏ ثُمَّ كَبَّرَ وَسَجَدَ فَكَانَتْ يَدَاهُ مِنْ أُذُنَيْهِ عَلَى الْمَوْضِعِ الَّذِي اسْتَقْبَلَ بِهِمَا الصَّلاَةَ ‏.‏

It was narrated that Wa'il bin Hujr said:"I came to Al-Madinah and said: 'I am going to watch the Messenger of Allah (ﷺ) pray. He said the takbir and raised his hands until I saw his thumbs near his ears. When he wanted to bow, he said the takbir and raised his hands. Then he raised his head and said: 'Sami Allahu liman hamidah (Allah hears the one who praises Him).' Then he said the takbir and prostrated, and his hands were in the same position in relation to his ears as when he started the prayer