Legality of making a sale before purchase under gst/indian law

Regards

is it legal if i

1. make a gst sale on 25 sept(example) to someone and pay tax for that while i don't already hold the sold stock/items/inventory.
2. delivery the goods to the person next month after making purchase and claim itc also next month.
3. so basically inventory for that specific item will be negative for that month closing. (not FY)

thanks