Luke 10:4
Carry no moneybag, no knapsack, no sandals, and greet no one on the road.
Jesus probably told the disciples to greet no one on the road, because the job they had to do was urgent and the time was short. There is a similar instruction given by Elisha to Gehazi in 2Kings 4:29
He said to Gehazi, “Tie up your garment and take my staff in your hand and go. If you meet anyone, do not greet him, and if anyone greets you, do not reply. And lay my staff on the face of the child.”
In both cases, the task at hand was too urgent for social chit-chat and precious time can easily get swallowed up by chatting.