Hazratjee, Moulana Maseehullah Khan Saaheb (rahmatullahi ‘alaih) mentioned:
The best of all deeds is to sit in the company of good, pious people and the worst deed is to sit with bad or evil people. Many a time people write to me saying: “My son was extremely obedient to me. He was punctual with his salaah. Suddenly his entire condition has changed so badly that he now has sarcastic answers for everything I tell him.” I then ask the person, “Is he hanging around with bad company?” Immediately the father will reply, “Yes this is the case.” (Hazrat Moulana Maseehullah Khan Saaheb [rahmatullahi ‘alaih] – A Brief Biography, pg. 206)