Shmuel Bais 18:33

And HaMelech was much moved, and went up to the aliyyat hasha'ar (upper room over the gate) and wept; and as he went, thus he said, O beni (my son) Avshalom, beni, beni Avshalom! If only I had died tachteicha (in place of, instead of) thee, O Avshalom, beni, beni!