Jabir b. Samurah said: The Messenger of Allah (ﷺ) entered upon us while the people were raising their hands. The narrator Zubair said: I think( they were raising the hands) during prayer. He (the prophet) said: What is the matter, I see you raising your hands as if they are the tails of restive horses! Maintain tranquility during prayer.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ النُّفَيْلِيُّ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا الأَعْمَشُ، عَنِ الْمُسَيَّبِ بْنِ رَافِعٍ، عَنْ تَمِيمٍ الطَّائِيِّ، عَنْ جَابِرِ بْنِ سَمُرَةَ، قَالَ دَخَلَ عَلَيْنَا رَسُولُ اللَّهِ صلى الله عليه وسلم وَالنَّاسُ رَافِعُو أَيْدِيهِمْ - قَالَ زُهَيْرٌ أُرَاهُ قَالَ - فِي الصَّلاَةِ فَقَالَ " مَا لِي أَرَاكُمْ رَافِعِي أَيْدِيكُمْ كَأَنَّهَا أَذْنَابُ خَيْلٍ شُمْسٍ اسْكُنُوا فِي الصَّلاَةِ " .
sunnah.com