What is the ruling on saying: "I will do such and such, or I will go to the market tomorrow," knowing that this is part of the unseen?

It is permissible to say: "I will do such and such," or "I will go to the market tomorrow," but it is better to follow it with the phrase: "In shaa Allah (if God wills)," due to the Almighty's saying: ﴿And never say of anything, "Indeed, I will do that tomorrow," Except [by adding], "If Allah wills."﴾