Salman Rushdie has described his morning routine in detail, most fully in a 2005 Paris Review interview, and it has stayed remarkably consistent across five decades of novels. The short version: he gets to the desk before the day gets to him, and he doesn't leave until he's earned the right to.

The Direct Answer
He writes first, before anything else, until he's put a few hundred words down.
That's the daily floor he described in his 2005 Paris Review interview, 'The Art of Fiction No. 186.'

Before Anything Else

His day starts before it really starts. Rushdie gets up, walks to his desk, and sits down still in his pajamas, before he's read a newspaper, opened his mail, phoned anyone, or often even showered. He's described this as giving the work 'the first energy of the day,' the idea being that sleep produces something usable and the surest way to waste it is spending the morning on anything else first. By one account, from interviewer Cal Fussman, who discussed the habit with him directly, that first stretch runs an hour or two before he does anything else, brushing his teeth included.

The session doesn't end on a clock. It ends when he decides something real has happened on the page, and until then, he stays put.

I do not let myself get up until I've done something that I think qualifies as working.

Salman Rushdie, The Paris Review, 'The Art of Fiction No. 186' (2005)

For how that first hour fits into the rest of his working life, see the full Salman Rushdie writing routine.

How Much Counts as Enough

Rushdie has been specific about what counts as enough on an ordinary day, and the bar he sets is low by design. 'I'm just looking for something that gives me a little rush, and if I can get that, get a few hundred words down, then that's got me through the day,' he told the Paris Review. A few hundred words is a small target for a novelist with his output. That seems to be the point: it's a target he can hit even on a slow day, and a daily practice needs exactly that kind of floor.

There's a second habit that shapes how the sessions connect. He reads through what he wrote the day before, first thing each morning, and returns to those same pages again that evening, before bed. The result is that he rarely starts cold. Momentum from the previous day carries into the next session before he's written a new sentence.

What You Can Steal