After Fajr & Maghrib Prayer
Muslim Taimi (R.A.) narrates from Prophet Mohammad (S.A.W.) to recite the following seven times before speaking to anyone:
اللَّهُمَّ أَجِرْنِي مِنَ النَّارِ
"O Allah, save me from the fire (Jahannam)."
If a person recites the above dua and dies the same night, he will be saved from Jahannam and if he recites it seven times after Fajr Salaat before speaking to anyone and if he dies on that same day, he will be saved from Jahannam.
In another hadith Prophet Mohammad (S.A.W.) stated that if a person recites the following dua 10 times while sitting in the Tashahudd position, then for each time ten rewards are written for him and ten sins are removed from the Name-Amal and he will be saved from every evil thing and the accursed Satan and no other sin besides shirk will be able to destroy him. In relation to actions, he will be superior to all other people. If anyone recites more than the above, he will go further and that is a different matter.
لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ بِيَدِهِ الْخَيْرُ يُحْيِي وَيُمِيتُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٍ
"Besides Allah there is no other worthy of worship. He is Alone and has no partner. His is the Kingdom and to Him is all praise, in His hands is good, He gives and takes life (gives death) and He has power overall things".