What is incumbent upon one who missed Fajr prayer on the bus and could not find anything with which to perform tayammum, should he pray while sitting without wudu or tayammum, or wait until he reaches the station?

Ablution (Wudu') is a condition for the validity of prayer (Salah (definition)). If water is not available, one may perform Tayammum (definition) (dry ablution). Praying on a bus or similar conveyances is not permissible due to the inability to fulfill its conditions. A Muslim must request to stop to perform the prayer. If this is not possible, or if one fears the prayer time will expire and it is impossible to perform ablution or Tayammum and pray with all its conditions, then one should pray according to their ability, and they must repeat the prayer upon disembarking. This is based on the Almighty's sayings: ﴿Allah does not burden a soul beyond its capacity﴾ and ﴿So fear Allah as much as you are able﴾. If the time for prayer arrives while one is riding and cannot disembark, they should pray on the conveyance, facing the Qiblah and fulfilling the pillars of prayer as much as possible, and repetition is obligatory. Praying on a riding animal in a state of safety is not permissible except for supererogatory (Nafl) prayers, unless one can perform the prayer completely. However, in a state of fear, it is permissible.