Is the water used to wipe the head during ablution considered altered by the cream or oil placed on the hair, and is it necessary to wash the head before ablution in this case?

The scholarly disagreement regarding water that changes due to a pure substance is valid. However, jurists have stipulated that if water changes due to a pure substance at the site of purification, it does not prevent the validity of the purification, as long as the water poured onto the limb is pure (tahur). So, if water changes on a limb due to a pure substance on it, like oil or other things, this does not prevent the validity of the purification. It is stated in Al-Mughni by Ibn Qudamah: "If there is a pure substance on the limb, such as saffron or dough, and the water changes due to it at the time of washing, it does not prevent the purification from being achieved; because it changed at the site of purification, similar to if the water used to remove impurity changed at its site." And in Kashshaf al-Qina': "If water changes due to saffron at the site of ablution or ritual bath, it remains pure (tahur) as long as it is at the site of purification, due to the difficulty of avoiding it."