this tradition was from hz. ibrahim as era, and a place in kaba called "cave of Kaba" used for this purpose, ppls come and make their mannat to allah and throught money and other things to cave of kaba, which called treasuer of kaba, in prophet's pbuh era such cave was closed and khazana-e-kaba transfered to a sahabi's home.
going to a cave for mannat! is that not shirk?