Fathwa - Is my fast broken if I fear that water was swallowed during gargling?

Question:
This morning I had to make ghusl. I am used to gargling very
'aggressively' and did so this morning while fasting. I felt that
something MAY have entered my throat but I am not sure if water went
DOWN. Is my fast invalidated?
Answer:
Walaikum assalam wa rahmatullah,
I pray this finds you in the best of health and spirits.
We assume our actions to be valid until we are sure otherwise, because
of the legal maxim that,"Certainty is not lifted by doubts." [Ibn
Nujaym, al-Ashbah wa'l Nadha'ir]
However, it is best not to gargle 'aggressively' when fasting, because
anything that endangers the validity of one's actions becomes
disliked.
And Allah alone gives success.