Ashvamedhika Parva 36.20

Those men who take birth in orders other than human beings, by growing up in view of the religions ceremonies of Brahmanas devoted to the duties of their own caste and desirous of doing good to all creatures, succeed through the help of such purificatory rites, in ascending upwards. Indeed, struggling, they at last attain the sam? regions with thcsc pious Brahmanas. Indeed, they go to the celestial region. This is the Vedic Shruti.