Question: If an ETF is Shariah-compliant, why would its income still require purification? 

Answer:

This is a reasonable question. Many Shariah-compliant equity standards allow investment in companies whose principal business activities are permissible, even if they earn a small amount of incidental income from non-permissible sources. For instance, a manufacturing company may produce entirely permissible goods but earn some interest from deposits held in a conventional bank. Provided that the company satisfies the applicable Shariah screening requirements, it may still be classified as Shariah-compliant.

One of the jurisprudential principles underlying this approach is يجوز تبعا ما لا يجوز استقلالا, meaning that what is impermissible independently may sometimes be tolerated when it is merely incidental or subordinate. This explains why directly investing in an interest-bearing instrument is different from investing in an otherwise permissible business that earns a limited amount of incidental interest. The concession, however, does not mean that the impermissible income itself becomes halal.

This is where investment purification becomes relevant. Rather than treating the entire investment return as impermissible, the portion attributable to non-Shariah-compliant sources is identified and removed. The investor may retain the permissible remainder. In this way, Shariah screening determines whether an investment is eligible, while purification addresses the treatment of any impermissible income arising from that investment.