Isaiah 56:6-7

Also the foreigners that join themselves to Jehovah, to minister unto him, and to love the name of Jehovah, to be his servants, every one that keepeth the sabbath from profaning it, and holdeth fast my covenant; even them will I bring to my holy mountain, and make them joyful in my house of prayer: their burnt-offerings and their sacrifices shall be accepted upon mine altar; for my house shall be called a house of prayer for all peoples.