ר' אבא בר נתן

Rabbi Abba bar Nathan [(see Rava bar Nathan) once lost his tefillin on a festival and came before Rabbi Chananiel, who sent to Rabbi Abba bar Nathan and said to him, "Give me your tefillin and go write for yourself." He said, "My master, go write for him." (Jerusalem Talmud, Chapter Those Who Shave, Halacha 4) (Sefer Mitzvot Gadol, Mitzvah 22, the version sent by Rabbi Chananiel to Rabbi). And it seems that he was writing tefillin.

And Rabbi Asi held that he was playing with them and became angry with him, and he died (Jerusalem Talmud, Nazir, Chapter 23, Halacha 2). The Rabbis of Kesar, Rabbi Chiya bar Abba in his name (Jerusalem Talmud, Chapter The One Who Releases, perhaps Isi his brother). And there is Rabbi Nathan bar Abba.]