Zayn Malik, Gigi Hadid ... In Case there Was Any Doubt ...

Zayn Malik and Gigi Hadid got all handsy with each other Saturday night, proving their relationship with clear and convincing evidence.

Zayn and Gigi left their favorite night spot -- The Nice Guy in WeHo at around 2:30 AM -- holding hands.

It's sort of a right of passage ... first going through back doors, then walking in separately, but eventually interlocking fingers.