Dua for Fasting
Fasting is not performed without intention. If a person stops eating and drinking without intention, his fast will not be valid. Intention is the intention of the heart. If you want to make an intention with your tongue, then after eating Suhoor or even before it, say this:
بِصَوْمِ غَدٍ نَوَیْتُ مِنْ شَهْرِ رَمَضَانَ