What is the ruling on paying zakat with the intention of both zakat and sadaqah?

Intention is a pillar of zakat which is an obligatory charity. It must therefore be paid only as zakat because it is not permissible to perform obligatory and voluntary acts of worship with one intention. Based on this, paying zakat with the intention of both sadaqah (which, unlike zakat, is a voluntary charity) and zakat is tantamount to paying it as sadaqah; its reward is one for a voluntary act of worship. Consequently, it must be repaid as zakat since the validity of its intention is contingent upon it being solely for the obligatory acts of worship. Imam Al-Nawawi said in Al-Majmu’:"If a person pays five dinars with the intention of paying the voluntary as well as the obligatory act of worship [sadaqah and zakat], he will be rewarded for the voluntary act of worship.”
And God the Almighty knows best.