What is the ruling on giving money to a person and commissioning him to buy something? Thank you.

It is permissible to give a person money to authorize them to buy or sell something, and this falls under the category of agency (wakalah) which is permissible by the Qur'an, Sunnah, and scholarly consensus. It is also permissible for the agent to buy goods with the given money, then sell them to the one who appointed them as agent after the goods have entered their possession.