If you are travelling after Fajr time, can you choose not to fast?

You must fast if travelling after Fajr. This is because one is only permitted to postpone the fast if he is a traveller at Fajr time. So even if you will be travelling later you must fast that day. Also, when you do travel later then you cannot break your fast.

فَمَنْ شَهِدَ مِنْكُمُ الشَّهْرَ فَلْيَصُمْهُ وَمَنْ كَانَ مَرِيضًا أَوْ عَلَى سَفَرٍ فَعِدَّةٌ مِنْ أَيَّامٍ أُخَرَ يُرِيدُ اللَّهُ بِكُمُ الْيُسْرَ وَلَا يُرِيدُ بِكُمُ الْعُسْرَ

So whoever amongst you witnesses the month, then let him fast. But whoever is unwell or on a journey, then (make up the) number (from) other days. Allah wills ease for you and does not will hardship for you. (Surah al-Baqarah, 185).

In the verse of the Holy Quran above, it is clarified that a person who is travelling has the dispensation of postponing the fast. However, the verse does not allow this for someone who will become a traveller later. Therefore, a person must fast if travelling after Fajr. Since he is not a traveller at the time of obligation, which is Fajr start time.

The verse does not permit a person to nullify or break a fast after having started it. This is why the Hanafi scholars explicitly mentioned the impermissibility of such actions. These are incredibly important rulings that many people are heedless of. Thus, they fall into sin due to ignorance.

قوله (والسفر) فيه أنه لا يبيح الفطر وإنما يبيح عدم الشروع في الصوم إذ لو كان السفر يبيح الفطر لجاز لمن أصبح مقيما ثم سافر الفطر مع أنه لا يجوز. (حاشية على مراقي الفلاح شرح نور الإيضاح)

His saying: travel. It means that it (travel) does not permit the nullification of a fast, rather it permits one to refrain from starting the fast. If it was the case that travel permits nullification then it would be permitted for someone who is resident and then travelled later, to nullify it. However, that is not permitted. (Imam al-Tahtawi, Haashiyah ala Maraaqi al-Falah).

السَّفَر لَا يُبِيحُ الْفِطْرَ، وَإِنَّمَا يُبِيحُ عَدَمَ الشُّرُوعِ فِي الصَّوْمِ، فَلَوْ سَافَرَ بَعْدَ الْفَجْرِ لَا يَحِلُّ الْفِطْرُ. (رد المحتار على الدر المختار)

Travel does not permit the nullification of a fast, rather it permits one to refrain from starting the fast. Therefore, if he travels after Fajr then nullification is not permissible. (Imam Ibn Abideen, Radd al-Muhtaar).

Thus, we see that a person who is a traveller at Fajr time is permitted to refrain from beginning the fast. However, he is not permitted to break (nullify) it after having started. If a person is not a traveller at Fajr time, then the obligation to fast remains, and it is unaffected by the fact that he will travel later in the day.

And Allah Most High Knows Best.

-Answered by Shaykh Noorud-deen Rashid (15.03.23)

See also:
Is it bad or wrong to miss fasts when travelling?

See also (video):