1. If you are performing a fardh ghusl, then ensure that water reaches every part of the body, especially the mouth, inside the nose, the corner of the eyes, inside the navel, etc. No part should be left dry. Even if an area equal to a hair’s breadth is left dry, the fardh ghusl will not be complete.
عن علي رضي الله عنه أن رسول الله صلى الله عليه وسلم قال من ترك موضع شعرة من جنابة لم يغسلها فعل بها كذا وكذا من النار قال علي فمن ثم عاديت رأسي ثلاثا وكان يجز شعره (سنن أبي داود، الرقم: 249)
Hazrat Ali (radhiyallahu anhu) reports that Hazrat Rasulullah (sallallahu alaihi wasallam) said, “The one who is in janaabah (requires a fardh ghusl) and leaves a portion (of his body) equal to a hair without washing it, that portion of his body will be subjected to such-and-such punishment in Jahannum.” Hazrat Ali (radhiyallahu anhu) thereafter said thrice, “That is why I dislike keeping hair.” It is reported that Hazrat Ali (radhiyallahu anhu) would shave his head (out of the fear that during the ghusl, no hair should remain dry, thereby causing the ghusl to be incomplete).