I came to the Prophet ﷺ from behind. I saw the whiteness of his armpits and he kept his arms away from his sides and raised his stomach (from the ground). (Using translation from Abū Dāʾūd 899)
أَتَيْتُ النَّبِيَّ ﷺ مِنْ خَلْفِهِ «فَرَأَيْتُ بَيَاضَ إِبْطَيْهِ وَهُوَ مُجَخٍّ وَخَرَّجَ يَدَيْهِ»