1 Timothy 4:1&3
Rome's Code of Canon Law (4:3:2:2):
Can. 1249 The divine law binds all the Christian faithful to do penance each in his or her own way. In order for all to be united among themselves by some common observance of penance, however, penitential days are prescribed on which the Christian faithful devote themselves in a special way to prayer, perform works of piety and charity, and deny themselves by fulfilling their own obligations more faithfully and especially by observing fast and abstinence, according to the norm of the following canons.
Can. 1250 The penitential days and times in the universal Church are every Friday of the whole year and the season of Lent.
Can. 1251 Abstinence from eating meat or some other food according to the prescripts of the conference of bishops is to be observed on ,of abstinence binds those who have completed their fourteenth year of age. The law of fasting, however, binds all those who have attained their majority until the beginning of their sixtieth year. Nevertheless, pastors of souls and parents are to take care that minors not bound by the law of fast and abstinence are also educated in a genuine sense of penance.
Can. 1253 The conference of bishops can determine more precisely the observance of fast and abstinence as well as substitute other forms of penance, especially works of charity and exercises of piety, in whole or in part, for abstinence and fast.