Śaṅkaraon Brahma Sūtra 3.4.38

Also for widowers, &c., the favour of knowledge is possible through special acts of duty, such as praying, fasting, propitiation of divinities, &c., which are not opposed to their ajrama-less condition and may be performed by any man as such. Thus Smr/ti says, ‘ By mere prayer no doubt the Brdhma//a perfects himself. May he perform other works or not, the kindhearted one is called Brdhma«a’ (Manu Sa;;/h. II, 87), which passage shows that where the works of the a^ramas are not possible prayer qualifies for knowledge. Moreover knowledge may be promoted by ajrama works performed in previous births. Thus Smr/ti also declares, ‘ Perfected by many births he finally goes the highest way’ (Bha. Gitd VI, 45); which passage shows that the aggregate of the different purificatory ceremonies performed in former births promotes knowledge.—Moreover knowledge—as having a seen result (viz. the removal of ignorance)—qualifies any one who is desirous of it for learning and so on, through the mere absence of obstacles. Hence there is no contradiction in admitting qualification for knowledge on the part of widowers and the like.