It was narrated from Jabir bin ‘Abdullah that the Messenger of Allah (ﷺ) said:“There is no Muhrim (pilgrim in Ihram) who exposes himself to the sun all day for the sake of Allah, reciting the Talbiyah until the sun goes down, but his sins will disappear and he will go back like on the day his mother bore him.”

English translation · Sunan Ibn Majah