How do you say bye in Afghanistan?

Salaam,

I am not sure, but I think they say "Khuda Hafiz", which means "May God be your protector." It is a Persian phrase which is used in Iran, Tajikistan, Pakistan, some parts of India, and I believe in Afghanistan. Iran, Tajikistan and Afghanistan are three countries where Farsi (Persian) is mainly spoken. Hope that helps!

Khuda Hafiz!