How did Umar ibn al-Khaṭṭāb perform ablution before his conversion to Islam in order to touch the scripture that contained Qur'an?

The sister of Omar (may Allah be pleased with him) commanded her brother to perform a ritual bath (ghusl) as one would for major ritual impurity (janabah) when he requested the scripture from her. She justified this by stating that he was impure due to his polytheism and that only the pure may touch it. This occurred at the beginning of Islam when legislation was not yet complete.