What is the appropriate dress for prayer according to the Sunnah of the Prophet, peace and blessings be upon him, and does wearing a short-sleeved shirt and uncovering the head affect the reward of prayer?

Allah Almighty commanded that one should take their adornment at every masjid. Thus, the worshipper is required to beautify themselves for prayer, in addition to covering their awrah. This adornment varies according to the custom of each country. If the custom of the people of a country considers covering the head and wearing a long-sleeved garment as part of adornment, then praying in a short-sleeved garment or bareheaded would be contrary to the divine command, even if the prayer is valid. However, if the custom of the people of a country considers that to be part of adornment, then there is no harm in praying in such attire, while keeping in mind that the garment of adornment may differ from home or sleepwear.

Sheikh Ibn Baz clarified that there is no harm in praying bareheaded, and that wearing a turban is better if it is among the usual adornments in that country. He also stated that those in a state of ihram (definition) pray with uncovered heads, which indicates the permissibility of doing so. Sheikh Ibn Uthaymeen added that covering the head is better if it is considered adornment among a certain people, otherwise not.