Answered by Shaykh Amjad Rasheed
How does one intend to fast? What are its conditions?
Whoever wants to fast the obligatory fast of Ramadan, it is obligatory that he intend to fast, that he specify it and that he bring to mind fasting the following day of Ramadan, and this suffices.
However, if he wants what is best and more complete, then, he should bring to mind and pronounce with his tongue, I intend to fast tomorrow as a current performance of the obligation of Ramadan in the present year for Allah Most High.
It is also a condition for a fast of Ramadan that the intention be made at night, meaning that it is made in any part of the night, even if just before dawn, because of his saying, peace and blessings be upon him in the rigorously authenticated hadith, Whoever does not intend the fast before dawn, has no fast.
So from this, whoever goes to sleep without making his intention and then wakes up after dawn, there is no fast for him on that day. However, it is still obligatory for him to stay away from those things which break ones fast, and he must also make up that fast after Ramadan.
[Translated by Sr. Shazia Ahmad]