Why does this hadith say that wearing perfume is allowed while in Ihram state?

It's stated in Saheeh Muslim (source ) that > 'A'isha (Allah be pleased with her) reported that when the Messenger > of Allah (ﷺ) intended to enter upon the state of Ihram he perfumed > himself with the best of perfumes which he could find and after that I > saw the glistening of oil on his head and beard. But I have heard that wearing perfume is not allowed if someone was in ihram state. What's the case here ?