When Malik bin Dinar saw a man pray improperly, he said:

“I feel pity for his children!”  He was asked, “He does not pray properly and you feel pity for his children?”
Malik said, “He is their chief (teacher) and they learn from him!”

Sifatus-Safwah, vol 3, p. 287

(Read on pg 29, Abdul-Malik Al-Qasim, Kindness to Parents. Darus-us-Salam. Riyadh: 2004.)