A Summary of the Fundamentals of Ahl al-Sunnah:
Among the essential requirements of fasting
is that the God-consciousness (taqwa) it cultivates
obliges a person to exhibit good character,
and to refrain from false speech and foolish behavior toward others;
otherwise, fasting will not yield its intended fruit.
The Prophet (peace and blessings of Allah be upon him) said:
"When any of you is fasting on a given day,
he should neither indulge in obscenity nor raise his voice in anger.
And if someone insults him or picks a fight with him,
let him say, 'I am a fasting person.'"
Agreed upon.
A Summary of the Fundamentals of Ahl al-Sunnah.