What does baba then do that shocks amir?

Baba shocks Amir by letting Hassan and Ali stay at the house, as Amir had put the wristwatch and Afghani bills under Hassan's mattress so that when Baba did find out about Hassan's stealing (a trait that Baba once told Amir he would never forgive in a person), Baba would want to push them out. Instead of Baba kicking them out, he forgave Hassan for "stealing" (he only admits stealing from Amir to protect him), and begs them to stay. Hassan and Ali leave the next morning and Baba weeps when they leave.