There is broad leeway in this matter, since no clear textual evidence has been established.
“He should apply oil every other day and apply kohl an odd number of times, …”
His statement, “He should apply oil every other day,” means using oil on one’s hair.
His statement, “every other day,” means that he does it one day and does not do it the next. It need not follow this exact sequence: he may use it one day and leave it for two days, or the reverse. But he should not use it continually, for then he would be among those given to luxury, who concern themselves only with the affairs of their bodies. This is not praiseworthy. Abu Dawud and al-Nasa’i relate that the Prophet, peace and blessings be upon him, forbade excessive indulgence in luxury (1)—that is, one should not excessively pamper oneself.
He, peace and blessings be upon him, also said: “The best of you are my generation, then those who come after them, then those who come after them. Then after them there will be people who give testimony without being asked to testify, betray trusts and are not trusted, make vows and do not fulfill them, and obesity will become prevalent among them” (2).
Obesity results from excessive indulgence in luxury, for one who does not pamper himself will generally not become obese. This indicates that excessive luxury is not praiseworthy.
Yet abandoning the use of oil altogether is also bad, because the hair will become disheveled and unattractive. A person should therefore take a middle course between these two extremes.
His statement, “and apply kohl an odd number of times,” refers to applying kohl to the eyes.