A person is hidden beneath his tongue.
المرء مخبوء تحت لسانه
El-mer'ü mahbûun tahte lisânihî
Ali ibn Abi Talib, Nahj al-Balagha, saying 148 (compiled by al-Sharif al-Radi); the same sentence also appears in saying 392.
The way to know a person is to let him speak.
The tongue opens the inner world.
As much as what he says,
how he says it,
and which word he avoids, give him away.
It is also a warning.
What you say
sometimes shows you your own inside.
The tongue is both mirror and veil.
The treasure stands between the two.