What is the expiation for one who forgot pebbles from Muzdalifah in his pocket, then lost them after returning to his country?

Scholars have differed regarding the ruling on taking stones or soil from the Haram. Some have prohibited it and mandated the return of what was taken, while others have deemed it disliked, and some have permitted it. There is no sin or expiation for one who forgets a pebble taken from Muzdalifah in their pocket, due to the Prophet's (peace be upon him) saying: "Indeed, Allah has pardoned for my Ummah their mistakes, their forgetfulness, and what they are coerced into."