pre_update_option_sidebars_widgets

See hook in action

See this hook used in plugins:

Select Pluginjetpack.9.8jetpack.9.8.1jetpack.9.9jetpack.9.9.1jetpack.10.0jetpack.10.1jetpack.10.2jetpack.10.2.1jetpack.10.7jetpack.10.9jetpack.11.0jetpack.11.1jetpack.11.1.2