Matthew 9:14

Then came to him the disciples of John; saying, Wherefore do we and the Pharisees fast much, and thy disciples fast not?

Matthew 11:2

And John having heard in prison the works of Christ, having sent two of his disciples,

John 3:25

Then was there an investigation of John's disciples with Jesus about purification.

John 4:1

Therefore when the Lord knew that the Pharisees heard that Jesus makes and baptizes more disciples than John,

Proverbs 20:6

The multitude of man will call each his mercy: and a man of faithfulness who shall find?

Matthew 6:16

And when ye fast, be not, as hypocrites, of gloomy aspect: for they conceal their faces that they might appear to men fasting. Verily I say to you, That they have their reward.

Matthew 11:18-19

For John came neither eating nor drinking, and they say, He has an evil spirit.

Mark 2:18-22

And the disciples of John, and of the Pharisees were fasting: and they come and say to him, Why do the disciples of John, and of the Pharisees fast, and the disciples to thee fast not?

Luke 5:33-39

And they said to him, Wherefore do the disciples of John fast frequently, and make prayers, and likewise they of the Pharisees; and they to thee eat and drink

Luke 18:9-12

And he spake to certain trusting upon themselves that they were just, and setting at nought the rest, this parable:

Treasury of Scripture Knowledge

Summary

Then came to him the disciples of John, saying, Why do we and the Pharisees fast oft, but thy disciples fast not?

Bible References

Why

Matthew 6:16
And when ye fast, be not, as hypocrites, of gloomy aspect: for they conceal their faces that they might appear to men fasting. Verily I say to you, That they have their reward.
Matthew 11:18
For John came neither eating nor drinking, and they say, He has an evil spirit.
Proverbs 20:6
The multitude of man will call each his mercy: and a man of faithfulness who shall find?
Mark 2:18
And the disciples of John, and of the Pharisees were fasting: and they come and say to him, Why do the disciples of John, and of the Pharisees fast, and the disciples to thee fast not?
Luke 5:33
And they said to him, Wherefore do the disciples of John fast frequently, and make prayers, and likewise they of the Pharisees; and they to thee eat and drink
Luke 18:9
And he spake to certain trusting upon themselves that they were just, and setting at nought the rest, this parable: