"The Messenger of Allah ﷺ came out to us and we were raising our hands during the Salah. He said: 'Why are you raising your hands while praying, like the tails of wild horses? Stay still when you are praying.'" (Using translation from Nasāʾī 1184)
خَرَجَ عَلَيْنَا رَسُولُ اللهِ ﷺ وَنَحْنُ يَعْنِي رَافِعُو أَيْدِينَا فِي الصَّلَاةِ فَقَالَ «مَا لَهُمْ رَافِعِينَ أَيْدِيَهُمْ فِي الصَّلَاةِ كَأَنَّهَا أَذْنَابُ الْخَيْلِ الشَّمْسِ اسْكُنُوا فِي الصَّلَاةِ»