Yazid bin Abi Ziyad said: Someone who saw Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) told me; he said: It is as if I am still looking at him while he was in prostration, keeping his elbows so far away (from his sides) that I could almost see the whiteness of his armpits.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8931