Rabbi Isaac the smith or Isaac Nappaha (Hebrew rav Yitzhak nappaha, רבי יצחק נפחא) was a second generation Galilean Amora. He was a pupil of Johanan bar Nappaha, "son of the smith" Tradition records him teaching in Antioch.Karaite tradition, borrowed from the Rabbanites, credits Isaac with the initiation of the month not by observing the moon, but like the Rabbanites computing according to the rule of lo, bet, dalet, waw which meant that the Passover can never begin on a Monday, or a Wednesday, or a Friday. To Isaac is attributed the parable of forcing a choice between halakhic and haggadic instruction as akin to pulling out both white hairs and black hairs till a man is left bald.
^Markus N. A. Bockmuehl Jewish law in gentile churches - Halakah and the Beginning of Christian Public Ethics. Grand Rapids: Baker, 2003, Page 54 "Indeed, Antioch continued for several centuries to serve as a place of residence for important religious leaders; even in the Amoraic period famous Rabbis like Simlai and Isaac Nappaha are sometimes cited as teaching in the city."
^Moshe Gil, David Strassler Jews in Islamic countries in the Middle Ages Page 224 - 2004 "The Karaite tradition (evidently borrowed from the Rabbanites) about R. Isaac Nappaha ('the smith'): "....the accepted custom was to fix the beginning of ..month by observing the moon, but they (the Rabbanites) began fixing the compute according to the rule of lo, bet, dalet, waw (ie, that the Passover shall never begin on a Monday, or a Wednesday, or a Friday), whose origin is unknown.. This is the method invented by Isaac Nappaha,.. "
^Faith and thought: journal of the Victoria Institute Volumes 93-95 Victoria Institute (Great Britain) - 1963 "Rabbi Isaac the Smith was beset by two eager junior colleagues, one of whom wanted Halakhic or legal instruction, the other Haggadic or homiletical. Each kept rudely pressing his own requirements, wherupon the older man rebuked them by personal parable. A middle-aged man, he said, had two wives, one his senior, one his junior. The younger wife, wishing her husband to look more her own age, kept pulling out his white hairs — the older lady, with the same motive in directional reverse, kept pulling out his black ones. But the poor man was merely left bald"
^Alfred J. Kolatch, Who's who in the Talmud- 1964 Isaac Nappaha A Palestinian Amora of the third and fourth centuries who was a pupil of Johanan. ... An older, wealthy Amora, named Isaac, is sometimes confused with Isaac Nappaha. Isaac Nappaha was an authority on haggadah and halachah. Once, Ammi and Assi would not let him speak because one insisted that he lecture on halachic matters , while the other wanted the discourse to be on haggadic matters.