The Way of Kings · Chapter 44
Shallan Steals Jasnah's Soulcaster
After witnessing Jasnah kill four attackers with her Soulcaster, Shallan swaps the fabrial with a broken one, betraying her mentor to save her family.
Outcome
Shallan gains the ability to Soulcast but is consumed by guilt, while Jasnah remains unaware of the theft.