Shaykh Abdul Muhsin al-Abbaad was asked:
What is the ruling on writing with the left hand?
“if a person is need of that or his hand is accustomed to that, then there is no harm. If he is capable of writing with this right hand, then it is not allowed for him to use the left with the ability to use the right”
[Sharh Sunan Abu Dawood no. 464]
Faisal Ibn Abdul Qaadir Ibn Hassan