Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates: It is the Sunnah that when a man is about to enter ihram, he should first take a ritual bath (ghusl).
Al-Bazzar, and al-Tabarani in al-Mu'jam al-Kabir, recorded it, but he (al-Tabarani) transmitted these words: (He should take a bath) at the time of entering ihram and at the time of entering Makkah. All of al-Bazzar's narrators are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الحج / 5323