Narrated Abdullah ibn Abbas:

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).

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ النُّفَيْلِيُّ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا أَبُو إِسْحَاقَ، عَنِ التَّمِيمِيِّ الَّذِي، يُحَدِّثُ بِالتَّفْسِيرِ عَنِ ابْنِ عَبَّاسٍ، قَالَ أَتَيْتُ النَّبِيَّ ﷺ مِنْ خَلْفِهِ فَرَأَيْتُ بَيَاضَ إِبْطَيْهِ وَهُوَ مُجَخٍّ قَدْ فَرَّجَ بَيْنَ يَدَيْهِ .