Is it obligatory to rinse the hair three times in Ghusl al-Janabah, or is once sufficient with the strong presumption that water has reached the roots of the hair?

"Running fingers through the hair during ghusl (definition) is a point of scholarly disagreement. What is obligatory in ghusl for janabah (definition) is to ensure water reaches the roots of the hair. If this can be achieved without running fingers through it, then doing so is recommended. However, if it cannot be achieved except by running fingers through it, then it becomes obligatory. A strong presumption that water has reached the roots of the hair is sufficient."