NKJV - 6 Now when they had gone through Phrygia and the region of Galatia, they were forbidden by the Holy Spirit to preach the word in Asia.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
It looks to me that John the evangelist was entrusted with Asia. As we see in Revelation 1:4 John writes to the seven churches in Asia which he had established.