Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
The sole fast required by the law of Moses was that of the great Day of Atonement (q.v.), Lev. 23:26-32. It is called "the fast" (Acts 27:9).
The only other mention of a periodical fast in the Old Testament is in Zech. 7:1-7, 8:19, from which it appears that during their captivity the Jews observed four annual fasts.
There was in addition to these the fast appointed by Esther (Esther 4:16).
Public national fasts on account of sin or to supplicate divine favour were sometimes held.
There were also local fasts.
There are many instances of private occasional fasting (1 Sam. 1:7, 20:34; 2 Sam. 3:35, 12:16; 1 Ki. 21:27; Ezra 10:6; Neh. 1:4; Dan. 10:2, 3). Moses fasted forty days (Ex. 24:18, 34:28), and so also did Elijah (1 Ki. 19:8). Our Lord fasted forty days in the wilderness (Mt. 4:2).
In the lapse of time the practice of fasting was lamentably abused (Isa. 58:4; Jer. 14:12; Zech. 7:5). Our Lord rebuked the Pharisees for their hypocritical pretences in fasting (Mt. 6:16). He himself appointed no fast. The early Christians, however, observed the ordinary fasts according to the law of their fathers (Acts 13:3, 14:23; 2 Cor. 6:5).