Albert Barnes on Luke 23:12

Made friends together, &c. What had been the cause of their quarrel is unknown. It is Commonly supposed that it was Pilate's slaying the Galileans in Jerusalem, as related in Lk 13:1,2. The occasion of their reconciliation seems to have been the civility and respect which Pilate showed to Herod in this case. It was not because they were united in hating Jesus, as is often the case with wicked men, for Pilate was certainly desirous of releasing him, and both considered him merely as an object of ridicule and sport. It is true, however, that wicked men, at variance in other things, are often united in opposing and ridiculing Christ and his followers; and that enmities of long standing are sometimes made up, and the most opposite characters brought together, simply to oppose religion. Comp. Ps 83:5-7.

(q) "friends" Acts 4:27