Ruling on employee selling an air travel ticket or exchanging it for a cheaper airline
Question

I work for an agricultural company, and they give me a ticket to travel to my city with a specific travel company. Is it permissible for me to book with this company, then cancel the booking and book with another company that costs less, and keep the difference? Or can I cancel the booking with the first company and travel by land, and keep the price of the air ticket?
Praise be to Allah.It is permissible for the employee who is given a travel ticket by his work to make use of the price of the ticket and travel by land, or travel on a different airline than the one for which he was given a ticket, and keep the difference between the two prices, unless his work does not allow that.
The basic principle regarding that is paying attention to what was agreed upon between the two parties, namely the employee and the workplace, because Allah, may He be exalted, says (interpretation of the meaning):
{O you who have believed, fulfill [all] contracts} [al-Ma’idah 5:1];
and the Prophet (blessings and peace of Allah be upon him) said: “The Muslims are bound by their conditions.” Narrated by Abu Dawud (3594); classed as sahih by al-Albani in Sahih Abi Dawud.
Shaykh Dr. ‘Abd al-Karim al-Khudayr (may Allah preserve him) was asked: Is it permissible to sell government airline tickets given to me, because I travelled by land?
He replied: There is nothing wrong with selling the tickets if you do not need them, unless travelling by land will result in you being late in returning to work. In that case, it is not permissible for you to travel except by the approved means of transportation, namely by plane. End quote.
And Allah knows best.