WPF EventToCommand

<Window ...
        xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
        xmlns:cmd="clr-namespace:GalaSoft.MvvmLight.Command;assembly=GalaSoft.MvvmLight.Platform"
        ...>
...
    <TabControl>
        <i:Interaction.Triggers>
            <i:EventTrigger EventName="SelectionChanged">
                <cmd:EventToCommand Command="{Binding TabSelectionChangedCommand}"
                                    PassEventArgsToCommand="True" />
            </i:EventTrigger>
        </i:Interaction.Triggers>

        <TabItem>...</TabItem>
        <TabItem>...</TabItem>
    </TabControl>
...
</Window>

---ref---
Use a Command with TabItem