Is it permissible to fast six days of Shawwal on Mondays and Thursdays with the intention of gaining the reward for fasting these two days?

There is no harm in fasting the six days of Shawwal on Mondays and Thursdays. By doing so, one earns the reward of fasting the six days and the reward of fasting Mondays and Thursdays. Sheikh Ibn Uthaymeen mentioned that if one's fasting of the six days coincides with a Monday or Thursday, they will receive the reward for both acts, by intending both, based on the Prophet's (peace be upon him) saying: "Indeed, actions are by intentions, and indeed every person will have what they intended."