Pasted

<ribbon:RibbonButton Label="OK" ToolTip="OK" Command="{Binding OkCommand}" CommandParameter="OK">
    <ribbon:RibbonButton.Style>
        <Style TargetType="{x:Type ribbon:RibbonButton}">
            <Setter Property="LargeImageSource" Value="/WpfRibbonButtonSample;component/Images/OkLargeIcon.png"/>
            <Style.Triggers>
                <Trigger Property="IsMouseOver" Value="True">
                    <Setter Property="LargeImageSource" Value="/WpfRibbonButtonSample;component/Images/OkLargeIconHot.png"/>
                </Trigger>
                <Trigger Property="IsEnabled" Value="False">
                    <Setter Property="LargeImageSource" Value="/WpfRibbonButtonSample;component/Images/OkLargeIconDisabled.png"/>
                </Trigger>
            </Style.Triggers>
        </Style>
    </ribbon:RibbonButton.Style>
</ribbon:RibbonButton>