I saw the whiteness of the side of the Messenger of Allah ﷺ while he was prostrating.
حدثنا يحيى بن إسحاق أخبرنا ابن لهيعة عن عبيد الله بن المغيرة سمعت أبا الهيثم يقول
رأيت بياض كشح رسول الله ﷺ وهو ساجد
No references are available.
Its chain of transmission is hasan. Ubaydullah bin Mughira is accepted (maqbul). Abu Haytham Sulayman bin Ubayd Atwari was raised in the household of Abu Saeed. Haythami likewise graded it hasan in al-Majma 2/125.It is indeed so, and it has many corroborating witnesses that are very strong. Among them is the hadith in Sahihayn, "When the Messenger of Allah ﷺ prostrated, he would spread his upper arms away from his sides until the whiteness of his armpits could be seen."