As-salamu ‘alaykum warahmatullaahi wabarakatuh,
“The angel can see what is in the heart of the human being, either because Allaah informs him of it or because Allaah has granted him some knowledge by means of which he is able to find it out.
The former view is supported by the report narrated by Ibn Abi’l-Dunya from Abu ‘Imraan al-Jawni who said: He calls out to the angel: Write down such and such for So and so, and he says: O Lord, he did not do it. He says: He intended it.
And it was said that the angel detects a foul odour when a person is thinking of doing a bad deed, and he detects a good smell for a good deed. That was narrated by At-Tabaraani from Abu Ma’shar Al-Madani. A similar report was narrated from Sufyaan Ibn ‘Uyaynah. “
Not a word does he (or she) utter but there is a watcher by him ready (to record it).
Fathul Baari by Ibn Hajar Asqalaani 11/325