The Messenger of Allah (ﷺ) said, "O people! Allah is Pure and, therefore, accepts only that which is pure. Allah has commanded the believers as He has commanded His Messengers by saying: 'O Messengers! Eat of the good things, and do good deeds.' (23:51) And He said: 'O you who believe (in the Oneness of Allah - Islamic Monotheism)! Eat of the lawful things that We have provided you..."' (2:172). Then he (ﷺ) made a mention of the person who travels for a long period of time, his hair are dishevelled and covered with dust. He lifts his hand towards the sky and thus makes the supplication: 'My Rubb! My Rubb!' But his food is unlawful, his drink is unlawful, his clothes are unlawful and his nourishment is unlawful, how can, then his supplication be accepted?"

[Muslim].