Salam, my brother. There are certain conditions for the shortened prayer. First of all I will give a reference from Quran about shortened prayers as:
Translation: "And when you travel throughout the land, there is no blame upon you for shortening the prayer, [especially] if you fear that those who disbelieve may disrupt [or attack] you. Indeed, the disbelievers are ever to you a clear enemy." (Surah no.4 ayyah no. 101)
This ayyah shows that it is not obligatory to shorten prayer rather it is a gift and ease from Allah. This point is clear from a Sahih Hadith as:
Sunan Abi Dawud 1199: Narrated Ya'la b. Umayyah:
I remarked to 'Umar al-Khattab: Have you seen the shortening of the prayer by the people today while Allah has said: "If you fear that those who are infidels may afflict you", whereas those days are gone now? He replied: I have wondered about the same matter for which you wondered. So I mentioned this to the Messenger of Allah (SAW). He said: It is an act of charity which Allah has done to you, so accept His charity.
So we should accept the charity from Allah otherwise, it would be counted as thanklessness. So, in journey we should preferably shorten our prayers because this is command of Prophet as "It is an act of charity which Allah has done to you, so accept His charity." And we must accept it. This means that during journey it is not endorsed to perform full length prayers.
As of you:
We often perform صلاة القصر (salatul qasr) while travelling. But sometimes, while returning from the tour, it becomes confusing that am I still مسافر (musafir) or not.
The answer of this, I will give is as below:
- When does shortening start
Remember journey starts when you leave your place towards a destination of about 48 miles or 77 kilometres as it is stated in Hadith:
The Prophet (PBUH) called a journey of one day & one night as travelling. Ibn Umar (RA), Ibn Abbas (RA) used to shorten the Salat & stop fasting in a journey of four ‘Burud’ i.e. sixteen ‘Farsakh’ i.e. 48 miles (1 Farsakh equals 3 miles). (Chapter 4, Book of Abridged Prayers, Sahih Bukhari, Vol. 2).
As you leave for journey, you will start shortening prayers until you reach your destination. When you reach there, you will continue shortening prayers until 19 days as it is stated:
Narrated by Ibn Abbas:
The Prophet once stayed for nineteen days and prayed shortened prayers. So when we travel led (and stayed) for nineteen days, we used to shorten the prayer but if we travelled (and stayed) for a longer period we used to offer the full prayer. (Sahih Bukhari Volume 2, Book 20, Number 186)
Now when you start coming back home you are still in journey until you step in your own house or residence as it is clear from here:
Once Ali(RA) left (Kufa) and started shortening the Salat (prayers) although the houses (of Kufa) were in sight. On his return he was told, "This is Küfa." (So that he would no longer shorten the Salat). He said, "No, [I will go on shortening the Salat (prayers)] till we enter Kufa. (Chapter 4, Book of Abridged Prayers, Sahih Bukhari, Vol. 2)
So I dont think there can be any confusion in presence of these Hadiths. Could I help you more? If any problem post in comments!