مَنْ قَالَ حِينَ يَدْخُلُ السُّوقَ لاَ إِلَهَ إِلاَّ اللَّهُ وَحْدَهُ لاَ شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ يُحْيِي وَيُمِيتُ وَهُوَ حَىٌّ لاَ يَمُوتُ بِيَدِهِ الْخَيْرُ كُلُّهُ وَهُوَ عَلَى كُلِّ شَىْءٍ قَدِيرٌ - كَتَبَ اللَّهُ لَهُ أَلْف...َ أَلْفِ حَسَنَةٍ وَمَحَا عَنْهُ أَلْفَ أَلْفِ سَيِّئَةٍ وَبَنَى لَهُ بَيْتًا فِي الْجَنَّةِ
‘Laa ilaaha illallaahu wahdahu laa shareeka lah, lahul mulku wa lahul hamdu yuhyee wa yumeetu wahuwa hayyun laa yamootu, biyadihi alkhayru wahuwa ala kulli shayyin qadeer’(There is none worthy of worship in truth except Allah alone, He has no partners, He has the dominion and for him is all the praise, He gives life and he takes life and he is the ever living and does not die, in his hand is goodness and he is capable of all things)
Allaah will write for him thousand thousand reward and erase from him thousand thousand sin and raise him thousand thousand and build for him a house in Jannah!”
[ Recorded in Sunan al-Nasa'ee (Eng ref: Vol. 3, Book 12, Hadith 2235) and Jami` at-Tirmidhi (3428); al-Jaami' as-Sagheer (v. 1 p. 1118) Shaikh al-Albaanee said the hadeeth is Hasan , Also classified as Hassan in Takhreej Mishkat al Masaabeh (2366) , Saheeh al Jaami' (6231) and Also recorded in Ibn Taymiyyah's book called " Gaining rewards" pg. 20]
Yaa SubhaanAllaah! Just by saying this one dhikr upon entering such a place you gain so much reward and get rid of so much sin! How merciful is Allaah!