Is someone who provided me with the contact information of a person for the purpose of buying a property from him entitled to a commission, even if he was unaware of the intention to buy and sell?

The act of mediating or brokering between a buyer and a seller is a contract known as brokerage (simsarah) or commission (ju'alah). For its validity, it requires an offer and acceptance, and a clear designation of the work and the fee. Merely providing someone's phone number is not considered work for which a fee is deserved, because "it involves no effort," and anything that involves no effort is not compensated.