There are numerous Bible portions that exhort people to fast. Jesus, speaking in Matthew 6:17 starts by saying “When you fast…” making clear that the expectation was that Gods people ARE fasting. Moses (Exodus 34:28), Esther (Esther 4:16), Daniel (Daniel 9) and even Jesus (Matthew 4:2) and Paul (Acts 9:18-19) all took time to fast. Other useful references are Judges 20:26-28, Joel 2:12, Jonah 3:5-10, Acts 13:1-3, among many others.