Anas ibn Malik Allah be pleased with him narrates that the Prophet, Allah send peace and blessings on him said, ”When a man leaves his house and says:

(I leave) in the name of Allah, I place my trust in Allah, there is no power (to stay away from sins) and no strength (to do good deeds) except with Allah’s assistance.

It is said at that moment in time, you have been guided, your needs have been taken care of and you have been protected. Then Shaytan moves away from him because he recited this Dua and another Shaytan says to him (to the Shaytan that moved away),how will you be able to misguide someone who has been guided, taken care of and protected?

حَدَّثَنَا إِبْرَاهِيمُ بْنُ الْحَسَنِ الْخَثْعَمِىُّ حَدَّثَنَا حَجَّاجُ بْنُ مُحَمَّدٍ عَنِ ابْنِ جُرَيْجٍ عَنْ إِسْحَاقَ بْنِ عَبْدِ اللَّهِ بْنِ أَبِى طَلْحَةَ
عَنْ أَنَسِ بْنِ مَالِكٍ أَنَّ النَّبِىَّ -صلى الله عليه وسلم- قَالَ: إِذَا خَرَجَ الرَّجُلُ مِنْ بَيْتِهِ فَقَالَ:

بِسْمِ اللَّهِ تَوَكَّلْتُ عَلَى اللَّهِ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ

قَالَ يُقَالُ حِينَئِذٍ هُدِيتَ وَكُفِيتَ وَوُقِيتَ فَتَتَنَحَّى لَهُ الشَّيَاطِينُ فَيَقُولُ لَهُ شَيْطَانٌ آخَرُ كَيْفَ لَكَ بِرَجُلٍ قَدْ هُدِىَ وَكُفِىَ وَوُقِىَ.

(رواه أبو داود، باب مَا يَقُولُ الرَّجُلُ إِذَا خَرَجَ مِنْ بَيْتِهِ، ح/٥٠٩٧)