Praise be to Allah.
Is ghusl necessary before ‘umrah?
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
“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.
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 .
Can you do ghusl one day before `Umrah?
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.” (Majmu` al-Fatwa, 10/22)
And Allah knows best.