When you finish the sunset prayer, say: 'O Allah, protect me from Hell" seven times; for if you say that and die that night, protection from it would be recorded for you; and when you finish the dawn prayer, say it in a similar way, for if you die that day, protection from it would be recorded for you. AbuSa'id told me that al-Harith said: The Messenger of Allah ﷺ said this to us secretly, so we confine it to our brethren. (Using translation from Abū Dāʾūd 5079)
"إذا انصرفْتَ من صلاة المغرب فقلْ: اللهمّ أَجرْنى من النّار سبعَ مرّاتٍ -فإنّك إذا قلتَ ذلك، ثم مُتّ في ليلتك كُتبَ لك جوارٌ منها- وإذا صليتَ الصبحَ فقلْ كذلك فإنك إنْ مُتَّ منْ يومكِ كتب لك جوارٌ منها".