Rihanna and Sia first collaborated when Sia wrote Riri's smash hit "Diamonds". Here is a leaked demo of another song that Sia wrote for Rihanna, which was said to be produced by David Guetta until Sia denied it on Twitter.
This is an unfinished version that still contains mostly Sia's vocals although Rihanna has started to replace it with her vocals that you can hear throughout the song, most prominantly in the second verse.
The final version would have been only Rihanna,