St Augustine of Hippo, born in 354 in what is now Algeria, was a Doctor of the Church famous for his enormous influence on Christian theology, especially the doctrine of original sin. (He is not to be confused with St Augustine of Canterbury, sent by Pope Gregory the Great to bring Christianity to Britain.)
The reference to 'a painting first seen with Carlo' is puzzling. There are two paintings by Botticelli entitled: 'St Augustine in his Cell.' One is reproduced here. The other can be seen on the Web Gallery of Art. (Click on the link and choose 'B' at the bottom of the page. Go to p.6 of the Bs, click Botticelli, then choose 'Paintings of religious subject-matter p.1. Scroll down to 'St Augustine.') There is a third painting: 'St Augustine in his Studio'.
However, all three are in Florence.