He is going to travel from one city to another and come back on the same day; can he break his fast?

The traveller is one of those to whom Allaah has granted a
concession allowing them to break the fast in Ramadaan. Allaah says
(interpretation of the meaning): 

“So whoever of you
sights (the crescent on the first night of) the month (of Ramadan i.e. is
present at his home), he must observe Sawm (fasts) that month, and whoever
is ill or on a journey, the same number [of days which one did not observe
Sawm (fasts) must be made up] from other days. Allaah intends for you ease,
and He does not want to make things difficult for you”

[al-Baqarah 2:185]

It makes no difference whether the journey is difficult or
easy. 

The scholars differed concerning the definition of what makes
a person a traveller and thus entitled to the concessions granted to
travellers, one of which is that a fasting person may break his fast. 

The majority of scholars define it in terms of distance,
which is approximately 80 kilometers. 

Others – and this is the view favoured by Shaykh al-Islam Ibn
Taymiyah – are of the view that what counts is ‘urf (custom – what is
customarily regarded as travel), and not the distance. 

So whatever people customarily regard as being travel is
travel, and comes under the rulings on travel in sharee’ah. 

Undoubtedly travelling from Amsterdam to Paris is something
that people would customarily regard as travel, even if one comes back the
same day. 

Shaykh Ibn ‘Uthaymeen said in al-Sharh al-Mumti’
(4/257) concerning a man who travelled a long distance in a short period: “A
short period for a long distance, such as one who travels from al-Qaseem to
Jeddah and back in one day – this is called travel, because people prepare
themselves for it and they think that they are travelling.” End quote. 

The distance between al-Qaseem and Jeddah is approximately
900 kilometers.  

Based on this, if a person travels from Amsterdam to Paris
and comes back the same day, he is travelling according to both scholarly
opinions, whether we base it on the distance or on what is customarily
regarded as travel. 

Is it better for him to fast or not to fast? 

The answer is: 

It is better for him to fast unless he finds it difficult, in
which case it is better for him not to fast. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: 

It is better for the traveller to fast, unless he finds it
too difficult, in which case he may break his fast. The evidence that it is
better for him to fast is as follows: 

1 – This is what the Messenger (peace and blessings of
Allaah be upon him) did. Abu’l-Darda’ (may Allaah be pleased with him) said:
We were with the Prophet (peace and blessings of Allaah be upon him) on
a hot day, such that one of us would lay his hand on his head because it was
so hot, and there was no one among us who was fasting except the Messenger
of Allaah (peace and blessings of Allaah be upon him) and ‘Abd-Allaah
ibn Rawaahah. Narrated by Muslim. 

2 – If he fasts it will be easier for him, because making up
the fast may be more difficult – in most cases – than doing it at the proper
time. That is because if he fasts in Ramadaan he is fasting at the same time
as other people, and that will be easier for him. When Allaah enjoined
fasting on His slaves, He said (interpretation of the meaning): 

“ Allaah intends for you ease,
and He does not want to make things difficult for you”

[al-Baqarah 2:185]

3 – If he fasts Ramadaan whilst travelling, he will discharge
his duty more quickly, because no one knows what will happen to him after
Ramadaan, so fasting will discharge his duty more quickly. 

There is a fourth benefit, which is that if he fasts in
Ramadaan he will have fasted at the best time, which is Ramadaan. 

But if it is too difficult he should not fast when he is
travelling, because the Prophet (peace and blessings of Allaah be upon
him) saw a crowd around a man who was shaded from the sun. He said: “What is
this?” They said: “One who is fasting.” He said: “It is not righteousness to
fast when travelling.” He said that to one who fasted whilst travelling
although it was difficult for him. One day when the Prophet (peace and
blessings of Allaah be upon him) made a stop during a journey, those who
were fasting fell down because they were exhausted, whilst those who were
not fasting put up the tents and gave water to the travellers and animals.
The Prophet (peace and blessings of Allaah be upon him) said: “Today
the reward has gone only to those who are not fasting.” Narrated by Muslim. 

Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen,
19/question no. 112 

And Allaah knows best.