Hiyya b. Ashi (or Rav Hiyya b. Ashi;Hebrew: רב חייא בר אשי) was a second and third generation Amora sage of Babylon. In his youth he studied under Abba Arika, and served as his janitor.
In his service of Abba Arika he learned a lot of Halakhaic laws, which he transmitted to future generations. He stated for example that on Shabbat he would wash Abba Arika's clothes that were made of leather. From this statement, the Sages of Chazal concluded that the law of Melabain (Scouring/Laundering) on Shabbat does not apply on leather materials. He also stated that when he used to wake Abba Arika from his sleep, he would wash his hands, recite Birkat HaTorah, and only then would teach the lesson set. Hence, one should make a Birkat HaTorah also on the Talmud, and not only on the Bible. Later, R. Hiyya b. Ashi said, Abba Arike would wear the Tefillin, and then recite the Shema, and it is from that statement that the sages of Chazal have concluded that one should put on Tefillin before the Shema, even if it is already time for the Shema.
Most of R. Hiyya b. Ashi's statements are made in the name of his teacher Abba Arika, and on rare occasions in the name of Samuel of Nehardea. At times his own rulings are cited as well, and sometimes he disputes his teacher Abba Arika.
He was a colleague of Rav Huna and had debated him over rulings of their common Rabbi-teacher, Abba Arika.