How to Back jab+Short slide?(Frame on hit +1)

Back jab has frame on hit +1.
Short slide has startup frame 3.
with this reason, it should not be combos.
but i see this combo in list, so how to combo it?

Thank you.

on crouching opponent. Could’ve asked in the combo thread also

;o, i made a video of it

[media=youtube]m44uXmIQUkY[/media]

hope it helps