Doing ghusl when entering ihram is Sunnah. The Prophet (blessings and peace of Allah be upon him) took off his regular clothes and did ghusl for entering ihram. And Asma’ bint ‘Umays (may Allah be pleased with her) was bleeding following childbirth, and the Prophet (blessings and peace of Allah be upon him) told her to do ghusl and enter ihram. If a person does ghusl one day before entering ihram, that will not benefit him, but his Hajj or ‘Umrah will be valid, because doing ghusl is not a condition for Hajj or ‘Umrah; rather it is Sunnah -- if a person does it, he will be rewarded for it, but if he does not do it, there is no sin on him. End quote.