How do we make Intention for Fasting
Allahumma Asoomo Ghadal-laka-fagh feerlee Maa qaddamtu wa maa akhkhartu
“O Allah! I will Fast for You tomorrow, therefore forgive me my future & past sins”
This should be prayed if the niyyat is done at night. But if one makes the niyyat after dawn, then one should pray the same words, except, instead of ‘gadan’ one should pray ‘hazal yaum’.
Niyyat is the firm intention of the heart, praying the actual du‘a for niyyat is not necessary but Mustahab and is better to do so.
The time for niyyat for the Fast of Ramadhan is from sunset (the previous day) till just before noon.
There are other Fasts like Qadha of Ramadhan, Qadha of a Nafl Fast, etc, for which the niyyat should be done before dawn and not before noon.