Is it obligatory to perform the 'Asr prayer on the bus, or after disembarking, or upon arriving home?

It is better to perform the Asr prayer after disembarking from the bus and before boarding transportation home, in order to attain the virtue of praying at the beginning of its prescribed time. Delaying the prayer until reaching home is permissible if it will be prayed before its time expires. However, praying inside the bus without fulfilling its conditions and pillars is not valid, as long as you will disembark from the bus before the prayer's time expires.