The words of one of the salaf:
“One of the signs of proper understanding is when a slave takes care of his eemaan,
and pays attention to what decreases it, and knows when it increases and when it decreases,
and recognizes the temptation of Shaytaan when he comes to him.”
(Sharh Nooniyah Ibn al-Qayyim by Ibn ‘Eesa, 2/140).