Answered by Shaykh Amjad Rasheed
Is it an innovation for men not to cover their heads?
Walaikum assalam wa rahmatullah,
Covering the head with a cap or turban is a sunna for men, established through the practice of the Messenger of Allah (Allah bless him and give him peace). However, it is not obligatory. A man who leaves covering his head is not sinful, though he has left a Prophetic sunna.
It is especially emphasized for men to cover their heads during prayer, because uncovering ones head is irreverent, as stated by Shaykh Ibn Hajar [al-Haytami] in al-Tuhfa. He stated explicitly that it is disliked for men to pray with their heads uncovered.
– Amjad Rasheed
(Translated by Faraz Rabbani)