Prayer: Making a Sinful Intention on the Way and the Sixth Condition: Nomads
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1290
With regard to someone who has not travelled for a sinful purpose, if on the way he makes the intention of travelling the rest of the journey for a sinful purpose, he must perform tamām prayers. However, the prayers he performed in qaṣr form [before he changed his intention] are valid.
Sixth condition: one must not be a nomad, such as the desert dwellers who roam the deserts and stay wherever they find water and food for themselves and their animals, and after a while move to another place. Such people must perform tamām prayers on these journeys.