The following dua (prayers) are recited at the beginning and end of the fast to indicate and affirm the intention of the fast.
A person's intention when fasting, is to bring him/herself closer to God.
Dua (Prayer) at the Beginning of the Fast 
Wa bisawmi ghadinn nawaiytu min shahri ramadan
I intend to keep the fast for tomorrow in the month of Ramadan
Dua (Prayer) at the End of the Fast 
Allahumma inni laka sumtu wa bika aamantu wa alayka tawakkaltu wa ala rizq-ika-aftartu
O Allah! I fasted for You and I believe in You and I put my trust in You and I break my fast with Your sustenance
