Is income from retirement in Missouri Kansas or Missouri income? I live in Kansas but taught in Missouri. (Now retired)

I retired as a teacher in Missouri but live in Kansas.  Is the monthly retirement money considered as income from Missouri (where  I worked), or from Kansas (since I am retired and live in across the state line in Kansas)?  Will I need to file a Missouri State tax return or (since I have lived in Kansas all 12 months) is the money considered as Kansas income?