Abu al-‘Abbas reported: I asked Ja’far ibn Nasir, may Allah have mercy on him, about mindfulness. Ja’far said, “It is to be watchful over one’s innermost being, due to awareness of the Almighty Lord, with every thought.”
Source: al-Risālat al-Qushayrīyah 1/331
عن أبي الْعَبَّاس البغدادي قال سألت جَعْفَر بْن نصير رحمه الله عَنِ المراقبة فَقَالَ مراعاة السر لملاحظة الحق سبحانه مَعَ كُل خطرة
1/331 الرسالة القشيرية