The Prophet ﷺ said, "Each of you should remain upright in his prayer and not spread out his forearms like a dog."
حدثنا يزيد حدثنا شعبة عن قتادة
أن النبي ﷺ قال ليعتدل أحدكم في صلاته ولا يفترش ذراعيه كالكلب
Its isnad is sahih, it was previously mentioned at 12926.