Al-Muzzammil 73:6

Inna nashi-ata allayli hiya ashaddu wat-anwaaqwamu qeela

Indeed, the hours of the night are more effective for concurrence [of heart and tongue] and more suitable for words.

Truly, rising by night (for prayer of tahajjud) is the most effective way to subdue (one’s base self) and to make speech more upright.