Sayyiduna Samurah (may Allah be pleased with him) said: The Prophet (peace and blessings be upon him) would raise both his hands while delivering a sermon, until the whiteness of his armpits could be seen.
Al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy, except that I did not find (any account of) the narrator Muhammad bin Rashid al-Asbahani, who was al-Tabarani's teacher.