Assalamualaikum ustaz. Every day I’d travel from my house to work which is located approximately 120 km away. Is it permissible for me to perform jamak qasar due to the long-distance travel which is more than 2 marhalah?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
Among the blessings given by Allah SWT to this ummah is the facilitation of qasar or shortening of the four rakaat prayer to two rakaat as well as the permissibility of combining two prayer times. Combining the Zohor and Asar prayers and the maghrib and Isyak prayers. This is called jamak. Both these facilitations are permissible specifically for those who are travelling.
It is facilitation so that prayer can be performed anywhere even when one is travelling. This is based on the statement of Allah SWT:
وَإِذَا ضَرَبْتُمْ فِي الْأَرْضِ فَلَيْسَ عَلَيْكُمْ جُنَاحٌ أَن تَقْصُرُوا مِنَ الصَّلَاةِ
“And when you travel throughout the land, there is no blame upon you for shortening the prayer,” 
There are several conditions that must be fulfilled for qasar and jamak to be permissible. Among stated by jurists are:
- The qasar prayer is the obligatory four rakaat prayer.
- There is a purpose with any direction
- It is a permissible journey and not for transgression or sin
- The distance of travel must exceed 2 marhalah or approximately 82 kilometres. This is taqribi (approximation)
- Passed the state or area of the place of resident
- Has ample knowledge of the rulings pertaining to qasar and jamak prayer. 
Al-Khatib al-Syarbini when explaining the conditions that permit qasar and jamak, he stated that the travel must not be for the purpose of sin. Whether it is for obligatory travel such as for hajj or mandub such as visiting the grave of the Prophet PBUH or permissible such as for business. 
Imam al-Ramli stated the travel must be for obligatory, mandub or permissible reasons. The travel may also be makruh such as an alone journey at night. 
For the above question, one should be reminded that jamak and qasar prayer can only be performed at the workplace or during travels. Once he enters his residential area, it is impermissible to take the rukhsah and he has to pray the complete prayer.
Let us all end our discussion with the supplication:
رَبِّ اجْعَلْنِي مُقِيمَ الصَّلَاةِ وَمِن ذُرِّيَّتِي ۚ رَبَّنَا وَتَقَبَّلْ دُعَاءِ ﴿٤٠﴾ رَبَّنَا اغْفِرْ لِي وَلِوَالِدَيَّ وَلِلْمُؤْمِنِينَ يَوْمَ يَقُومُ الْحِسَابُ
“My Lord, make me an establisher of prayer, and [many] from my descendants. Our Lord, and accept my supplication. Our Lord, forgive me and my parents and the believers the Day the account is established.”
 See al-Taqrirat al-Sadidah fi al-Masa’il al-Mufidah, pg. 314-315
 See al-Iqna’ fi Hilli Alfaz Abi Syuja’, 2/384
 See Nihayah al-Muhtaj Syarh al-Minhaj, 2/248