How does one perform istinshaq (sniffing water into the nose) during wudu (ablution) and ghusl (ritual bath), and is it obligatory to make the water reach the upper part of the nose or is it sufficient for it to reach the middle? How is this done during fasting and when the nose is blocked?

"Istinshaq" (sniffing water into the nose) is the act of drawing water with the breath as far as possible into the nose to cleanse it. It is obligatory according to some scholars, and a Sunnah (definition) (recommended practice) according to others. Exaggerating in it is prescribed, except for a fasting person; for them, exaggeration is disliked, and a light drawing of water is sufficient. Similarly, when the nose is blocked due to a cold or similar condition, the drawing should be light. The evidence for its legality is the Hadith (definition) of Laqit ibn Sabira, narrated by Abu Dawud and Al-Tirmidhi.