Personalities of the Buddhist Suttas
From Kapilavatthu, he was of the Brahmin class. In SN V: The Great Chapter, there is a Chapter named after him. In Sutta X he describes his method of attainment: From being indifferent to Dhamma and the Order, he became acquainted with the Buddha, after this he developed strong feelings of respect and admiration for the Buddha, at that point he gave up the household life for the homeless life and developed understanding of the Khandhas: This is materiality, this is the arising of materiality, this is the ending of materiality ... sense experience ... perception ... confounding ... consciousness; Using this method he arrived at Streamwinning, seeing "This is Dukkha, this is the arising of Dukkha, this is the ending of Dukkha, This is the Way to the ending of Dukkha; at this point he concentrated on developing the seven dimensions of self-awakening: minding, investigation of Dhamma, Energy building, Entheusiasm, Impassivity, High-Getting, and Detachment and by that realized Arahantship.
Udayi discusses the Buddha's method of teaching that consciousness is not the self in SN 4.35.193 and converts the Nobel Lady of the Verahaccani clan by a demonstration of the great respect that is to be shown for the Dhamma in Sanyutta Nikaya, Part IV, Salayatana group #133 (10)[SN 4.35.133]. Verahaccani, translated here at: DhammaTalk: Dhamma Talk: Respect Worthy Dhamma
PTS: The Book of the Kindred Sayings V: Kindred Sayings on the Limbs of Wisdom: Udayi, Woodward, trans., pp 74
WP: The Connected Discourses of the Buddha, II, Udayi, Bhk. Bodhi, trans., pp1588