Purify wealth follow up

Slms can you kindly confirm if the shares are halal why would we have to purify our wealth.

Wa alaykum salaam,

A particular Shares investment maybe halal overall but a very small proportion of income maybe from non halal sources.

oh I never knew this. Jazakallah for the response.
How would a person know how much of the halal share is dealing in a non halal source.
Please kindly confirm. Jazakallah

Wa alaykum salaam,

This knowledge can be acquired from various stock screening apps and platforms.