If a traveller is not sure whether he should fast or not, then he decides to fast after dawn breaks
Question

A few years ago I went for ‘umrah with my brother and his wife during Ramadan, and I did not know whether they would be fasting whilst travelling or not, and I felt too shy to ask them. I thought: if they fast, I will fast with them, and if they break the fast I will break the fast with them. When dawn broke, I was still hesitating whether to refrain from eating or not, then my brother told me that they were fasting, at which point I intended to refrain from eating, but that was after the sun rose. A few days ago I read that in order to fast, one should form a firm intention before dawn. So I decided to fast that day and I did fast it. My question is: do I have to offer expiation as well or not, because that was five years ago? My second question is: I seem to remember that my sister was also hesitant. Should I tell her that she has to make up the fast or not, because I am not sure that she was hesitant like me, and I am afraid that she will tell me that this is waswaas (whispers from the shaytaan).
Praise be to Allah.In order for an obligatory fast to be valid, it is essential that the intention be formed the night before, because the Prophet (blessings and peace of Allah be upon him) said: “Whoever did not intend to fast before Fajr, there is no fast for him.” Narrated by Abu Dawood (2454), at-Tirmidhi (730), an-Nasaa’i (2332). According to a version narrated by an-Nasaa’i: “Whoever does not form the intention to fast before Fajr, there is no fast for him.” This hadith was classed as saheeh by al-Albaani in Saheeh Abi Daawood. So if someone is still hesitant when dawn breaks, and he is not sure whether he is going to fast or not, his fast is not valid.
It says in Asna’l-Mataalib (1/411): When fasting, it is essential to have a firm and specific intention, as in the case of the prayer, because of the report: “Actions but by intentions…” The intention must be formed before Fajr in the case of an obligatory fast, whether it is in fulfilment of a vow, making up a missed fast (qada’) or an expiatory fast (kafaarah). End quote.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: If a person who is permitted not to fast says on the first night of Ramadan: Maybe I will fast tomorrow and maybe I will not fast, then he decides after dawn has broken to fast, his fast is not valid, because of his hesitation in forming the intention.
End quote from ash-Sharh al-Mumti‘ (6/362)
Based on that, what you must do is make up this day, and you have done well in that regard.
You do not have to offer any expiation, because expiation is only required in the case of a non-traveller who breaks the fast during the day in Ramadan by having intercourse.
See the answer to question no. 49750.
If your sister fasted when she was hesitant, then she must make up the fast, and you should inform her of that.
And Allah knows best.