Bismillah,
:salam2:
If one can not determine the direction of the qiblah
He should ask one who knows. If he finds no one to ask, he should try his best to determine it. In such a case, his prayer will be valid, and he need not repeat it even though he discovers later on that he had faced in the wrong direction. If it is made clear to him while he is praying that he is facing the wrong direction, he need only turn in the proper direction without stopping his prayer. This is based on the following incident: Ibn 'Umar reported that the people were praying the morning prayer in the Quba' mosque when a person came to them and said, "Allah has revealed some of the Qur'an to the Prophet in which we have been ordered to face the Ka'bah, so face it." They immediately turned their faces from Syria to the Ka'bah." (Related by al-Bukhari and Muslim.)
If one prays according to what he determined and then wants to make another prayer, he should again try to determine the qiblah's direction. If it turns out to be different from what he had determined earlier, he should pray in the new direction without repeating his earlier prayer
Vol 1, Book 8. Prerequisites Of The Prayer. Fiqh 1.115
Two cases in which one doesn't have to face the Ka'bah
The first one is performing voluntary prayers while riding (an animal, car and so on). The rider may bend his head slightly for the bowings and prostrations of the prayer, but he should bend a little bit lower for the prostrations. He may face in whatever direction his ride is going.
Reported 'Amr ibn Rabi'ah, "I saw the Messenger of Allah, upon whom be peace, pray while riding, and he faced the direction in which he was going." This hadith is related by Muslim, at-Tirmizhi and al-Bukhari. The latter added that "he bent his head slightly."
He did not, however, do this for the obligatory prayers. Ahmad, Muslim and at-Tirmizhi recorded that he would pray on his mount while travelling from Makkah to Madinah, facing away from Makkah. Upon this, Allah revealed, "Wherever you turn, you will find Allah's face." Says Ibrahim an-Nakha'i, "They would pray on their mounts and animals in the direction in which they were facing." Ibn Hazm comments, "This has been related from the companions and those of the following generation, during travel and residence. "
The second case is praying while having to deal with forced conditions, illness and fear. Under such circumstances, it is allowed to pray without facing the qiblah. The Prophet, upon whom be peace, said, "If I order you to do something, do what you are capable of doing." Says Allah, "If you go in fear, then (pray) standing or on your mounts..." (al-Baqarah 239). Ibn 'Umar added, "Facing the qiblah or not facing it." (Related by al-Bukhari.)
Vol 1, Book 8. Prerequisites Of The Prayer. Fiqh 1.115A.
Taken from Fiqh-us-Sunnah
I hope that was helpful, insha'Allah!
