“God heard the voice of the lad…” (Genesis 21:17).
After Sarah complained about Yishmael harassing their son Isaac, Abraham reluctantly sent Yishmael and his mother Hagar away. Lost in the desert and with their water used up, Hagar cast her son under one of the bushes and wept in a loud voice as she waited for him to die (Genesis 21:9-16).
The Kotzker Rebbe pointed out that scripture only speaks of Hagar crying and says nothing about her son crying. However, the verse says that God heard the voice of the lad.
He explained that sometimes, someone can cry from the deepest part of his soul without making a sound – but Hashem hears this cry.
The students of Rebbe Nachman of Breslov once asked him: How loudly should a person cry out to God in prayer? Rebbe Nachman said: So loud, that no one can hear him!