What is the ruling on greeting with a hand gesture?

Greeting with a gesture is not permissible. The Sunnah is to greet with words, both initiating and responding, because greeting with a gesture resembles some disbelievers and contradicts what Allah has legislated. However, if a Muslim gestures with his hand to convey his greeting due to the distance of the person being greeted, while also speaking the greeting, there is no harm. Likewise, the person being greeted may respond with a gesture if he is engaged in prayer, as the Sunnah has validated this.