In the first place, we would like to make it clear that a Muslim is always eager to perform his Prayer at its due to time, without any delay or hesitation, as Almighty Allah commands us.
Sheikh Muhammad Saleh Al-Munajjid, a prominent Saudi scholar and lecturer states that: Praying in cars, planes, trains or other means of conveyance, where one cannot face the direction of the qiblah or pray standing, is not permissible in the case of obligatory Prayers unless two conditions are met:
1. If you fear that the time for the obligatory Prayer will end before reaching your destination. But if you will reach your destination before the time for Prayer is over, you should wait until you get there to pray.
2. If it is not possible to get off and pray on the ground. If it is possible to do so, then you must do that.
If these two conditions are met, then it is permissible to pray in the vehicle. The evidence for it being permissible to pray in this case is the general meaning of the verses in which Allah says: “and [Allah] has not laid upon you in religion any hardship” (Al-Hajj: 78)
If it is said, If I am allowed to pray in these vehicles, should I face the qiblah and should I pray sitting even though I am able to stand? The answer is:
If you are able to face the direction of the qiblah throughout the Prayer, then you must do that, because it is a condition of an obligatory Prayer being valid whether one is traveling or not.
If it is not possible to face the qiblah throughout the Prayer, then fear Allah as much as you can and do your best, because of the evidence narrated above.
This has to do with obligatory Prayers. With regard to supererogatory (nafl) Prayers, the matter is more relaxed. It is permissible for the Muslim to pray in the vehicles mentioned no matter what direction they are facing, even if he could get down on the ground at some times, because the Prophet (peace and blessings of Allah be upon him) used to pray nafl Prayers on his mount no matter what direction it was facing. Jabir narrated that the Prophet (peace and blessings be upon him) “used to pray voluntary Prayers when he was riding without facing the qiblah.” (Narrated by al-Bukhari) But it is better to face the qiblah when starting to pray a nafl Prayer, if that is possible when traveling.
With regard to offering obligatory Prayers sitting down when one is able to stand, that is not permissible because of the general meaning of the verse in which Allah says: “And stand before Allah with obedience” (Al-Baqarah :238)
And because of the Hadith of `Imran ibn Husayn, according to which the Prophet (peace and blessings be upon him) said to him: “Pray standing; if you cannot, then sitting; and if you cannot then lying on your side.” (Narrated by al-Bukhari).