The Quran

إِنَّمَا النَّجوىٰ مِنَ الشَّيطانِ لِيَحزُنَ الَّذينَ آمَنوا وَلَيسَ بِضارِّهِم شَيئًا إِلّا بِإِذنِ اللَّهِ ۚ وَعَلَى اللَّهِ فَليَتَوَكَّلِ المُؤمِنونَ

Muhammad Asad

[All other kinds of] secret confabulations are but of Satan's doing, so that he might cause grief to those who have attained to faith; yet he cannot harm them in the least, unless it be by God's leave:¹ in God, then, let the believers place their trust!

I.e., in and by itself, the force of evil epitomized in the concept of "Satan" has no power whatever: cf. 14:22 - "I had no power at all over you: I but called you - and you responded unto me. Hence, blame not me, but blame yourselves." (See also Razi's views quoted in my note 31 on the above-mentioned verse.) As regards the problem of God's "letting" or "allowing" a person to go astray (implied in the phrase "unless it be by God's leave"), see note 4 on 14:4.