Jami` at-Tirmidhi Book 42, Hadith 27
"I entered upon the Messenger of Allah (ﷺ) while there was a scribe in front of him, and I heard him saying: 'Put the pen on your ear, for that is more conducive to the scribe remembering.'"
that the Messenger of Allah (ﷺ) said: "When one of you writes something, then let him Yutarrib (smeared with dust to dry the ink) it, for that is more conducive to the need."
"The Messenger of Allah (ﷺ) ordered me to learn some statements from writings of the Jews for him, and he said: 'For indeed by Allah! I do no trust the Jews with my letters.'" He said: "Half a month did not pass before I learned it, when he (ﷺ) wanted to write to the Jews I would write it to them, and when they wrote to him I would read their letters to him."