AkashG's solution don't work for me. When I set up check.xml to background it's just stratched in vertical direction. To solve this problem you should set up check.xml to "android:button" property:
<ToggleButton
android:id="@+id/toggle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:button="@drawable/check" //check.xml
android:background="@null"/>
check.xml:
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<!-- When selected, use grey -->
<item android:drawable="@drawable/selected_image"
android:state_checked="true" />
<!-- When not selected, use white-->
<item android:drawable="@drawable/unselected_image"
android:state_checked="false"/>
</selector>