It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that when the Prophet (peace and blessings be upon him) performed prostration, the whiteness of his blessed armpits could be seen.
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 3197
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف، التميمي مجهول