He never "said" it directly but it was made clear to the audience that he was going to do it as soon as Maul lifted Satine with a Force chock. Also, you have no proof that Maul didn't decide to kill Satine before he was "enraged"(hell, was already enraged).
Maul also did it to Bo-Katan like this, did he kill her? He was clearly trying to torture her to make Obi Wan succumb, that's a slow process to turn a Jedi so why would he kill Satine so soon rather than use her as a tool to keep torture Obi Wan.
If he wanted to kill her right way she would be dead in seconds after being choked rather than still have words to spill out. Clearly he's torturing her rather than wanted to kill her right here.