Isaiah 56:6-7

As for the foreigners who join themselves to the  LORD to minister to him, to love the name of the LORD, and to become his servants — all who keep the Sabbath without desecrating it and who hold firmly to my covenant — I will bring them to my holy mountain  and let them rejoice in my house of prayer. Their burnt offerings and sacrifices will be acceptable on my altar,  for my house will be called a house of prayer for all nations.”