In Vinayavastu there is the story of Sariputra's conversion to Buddhism, it says that he was searching for a teacher, and went to see all the famous teachers: Puranakasyapa, Maskari-gosaliputra, Sanjaya-vairatiputra, Ajita-kesakambala, Kakuda-katyayana, & Nirgrantha-jñatiputra. He asked them all two questions, and finally he became a disciple of Sanjaya-vairatiputra, who is designated as agnostic.
What immediately comes to mind is that Buddha Shakyamuni was at that time quite unknown! In Buddha's own words He was immensely famous during his six years of ascetism. But maybe wasn't famous at all during the next period of His life? Because Sariputra had never taught of visiting Him. And maybe not even heard of Him (after His enlightenment).
When seeing one of the first five disciples of Buddha, Sariputra asks: "Who is your teacher?" In outward appearance the Buddha's disciples were at that point similar to other Sramanas, thus it is taught normally, the patched robe was developed later. But even that may have been characteristic of Sramanas in general.
Before his conversion to the Dharma Sariputra was known as Upatisya, his Dharma name is Sariputra.
There is a book ( havent't read it): The Sutra on the foundation of the Buddhist Order (Catusparisatsutra): Relating the events from the Bodhisattva's enlightenment up to the conversion of Upatisya (Sariputra) and Kolita (Maudgalyayana), translated by Ria Kloppenborg

