Is it obligatory to put water into both nostrils when sniffing water in Wudu, or is one nostril sufficient, and what is required if one of the nostrils is blocked?

Inhaling water (Istinshaq) and expelling it (Istinthar) are obligatory in ablution. Istinshaq is introducing water into the nose. It is sufficient to introduce water into the inner part of the nose. A blocked nose due to illness does not pose a problem because it does not prevent the entry of water; rather, it prevents the non-obligatory exaggeration. However, if Istinshaq causes harm due to illness, its obligation is waived.