Abu Ishaaq al-Talhee said,

أن علي بن طالب كان يضرب الحسن و الحسين على اللحن

“‘Ali bin Abi Taalib would discipline Hasan and Husayn for mistakes in grammar.”

Source: al-Jaami’ (2/28) by Khateeb al-Baghdaadi

‘Amr bin Dinaar said,

أن ابن عمر و ابن عباس كانا يضربان أوالادهما على اللحن

“Ibn ‘Umar and Ibn ‘Abbas would discipline their children for mistakes in grammar.”

Source: al-Jaami’ (2/29) by Khateeb al-Baghdaadi