Mark 6:7
"And he called unto him the twelve, and began to send them forth by two and two; and gave them power over unclean spirits;"
Cross References (ranked by relevance)
Luke 10:1
After these things the LORD appointed other seventy also, and sent them two and two before his face into every city and place, whither he himself would come.
Revelation 11:3
And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.
Mark 16:17
And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;