Does a worshipper say one Taslima or two Tasleemas upon finishing the prayer?

The correct view is that the two salutations are necessary, based on the established hadiths from the Prophet, peace and blessings be upon him, regarding this, and his saying: "Pray as you have seen me praying." The opinion that one salutation suffices is weak. However, if someone does so out of ignorance or believing in the authenticity of hadiths supporting it, then their prayer is valid.