If we join the company of the lovers of Allah Ta‘ala, we will also be blessed and favoured. The third class of a train reaches wherever the first class reaches. A dog is impure and najis. However the dog that accompanied the Ashaab-e-Kahf (people of the cave), who were a group of lovers of Allah Ta‘ala, became so valuable that it has been mentioned in the Quraan Majeed which will be recited even in Jannat.
Source: Al-Haadi