All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is not permissible to use the greeting of Namaste as it is among the Hindu rituals, thus it involves imitating non-Muslims in matters that are peculiar to their religious rituals. It is confirmed that the Prophet said: “Whoever imitates a people is one of them.” In addition to this, it includes bowing (which is also forbidden). So it is not permissible even if it does not involve this bowing because it entails the imitation which we have mentioned.
For more benefit, please refer to Fatwa 155789.
It is not a condition to intend imitating them for it to be forbidden; rather, it is forbidden to imitate them even without having the intention to do so. Ibn Taymiyyah said about imitating non-Muslims: “A Muslim is not allowed to do what is peculiar to them whether he intends to imitate them or does not intend to do so, but does it according to the habit that he used to have.”
Ibn ‘Uthaymeen said: “If there is imitation then this is prohibited, and its ruling (that it is forbidden) is confirmed whether one did so with intention or without intention.”
Of course this cannot be compared to the Islamic expressions that the non-Muslims may use such as ‘insha-Allaah’ or ‘Alhamdulillaah’ as they thus say expressions of truth, so how can this be compared to expressions of falsehood?
Allaah Knows best.