I think the hadith you are looking for is:
ـ"وَحَدَّثَنَاهُ أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَمُحَمَّدُ بْنُ
بَشَّارٍ، كِلاَهُمَا عَنْ غُنْدَرٍ، - قَالَ أَبُو بَكْرٍ حَدَّثَنَا
مُحَمَّدُ بْنُ جَعْفَرٍ، غُنْدَرٌ - عَنْ شُعْبَةَ، عَنْ يَحْيَى بْنِ
يَزِيدَ الْهُنَائِيِّ، قَالَ سَأَلْتُ أَنَسَ بْنَ مَالِكٍ عَنْ قَصْرِ
الصَّلاَةِ، فَقَالَ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِذَا
خَرَجَ مَسِيرَةَ ثَلاَثَةِ أَمْيَالٍ أَوْ ثَلاَثَةِ فَرَاسِخَ -
شُعْبَةُ الشَّاكُّ - صَلَّى رَكْعَتَيْنِ" [صحيح مسلم ٦٩١].
I asked Anas b. Malik about shortening of prayer. He said: When the Messenger of' Allah (may peace be upon him) had covered a distance of three miles or three farsakh (Shu'ba, one of the narrators, had some doubt about it) he observed two rak'ahs. [Sahih Muslim 691]
Actually I don't know waht is the rule for your situation, but I quoted some of the questions that people asked Shayikh Mohammed bin Saleh bin Uthaymeen
Question1:Students go to study in a country, away from their own
residents about ninety kilometers, by knowing that they go and return
in the same day, Can they held jama and qasar?
He replied by saying: I
see that there is no held jama and qasar; because this is not
traveling, as they have their breakfast in their homes, and have their
lunch in their homes too. [Reference for fatwa in Arabic]
Question2: I work as a truck driver and requires me traveling always,
Can I held jama and qasar?
He replied by saying: shortening the
prayers related to travel so long, whether traveling rarely
or always, and the driver of truck can held jama and qasar. [Reference for fatwa in Arabic ]
And Allah knows best, Wa salla allah ala Mohammad.