Is it permissible to insert and move a finger in the navel during Ghusl to allow water to enter and ensure it reaches?

Overriding probability (Ghalabat al-Dhann) is sufficient for encompassing the body with water and ensuring it reaches all areas during ghusl (definition) (ritual bath), as it is considered equivalent to certainty (Yaqeen). The evidence for this is Aishah's narration describing the Prophet's ghusl (peace be upon him). Al-Shawkani said in his commentary: "This is proof that overriding probability regarding water reaching what must be washed is like certainty." It is also mentioned in the commentary of I'anat al-Talibin that overriding probability concerning water encompassing the entire limb is sufficient, and certainty is not required.