The Prophet ﷺ said: To harbour good thoughts is a part of well-conducted worship. (This is according to Nasr's version). Abu Dawud said: Mahna' is reliable and he is from Basrah.  

The Messenger of Allah (May peace be upon him) was in the I’TIKAF(seclusion in the mosque). I came to visit him at night . I talked to him, got up and turned my back. He got up with me to accompany me. He was living in the house of Usamah b. Zaid. Two men of the Ansar passed by him. When they saw the Messenger of Allah (May peace be upon him), they walked quickly. The prophet (May peace be upon him) said: Be at ease; she is Safiyyah daughter of Huyayy. They said: Glory be to Allah, Messenger of Allah! He said: The devil flows in man as the blood flows in him. I feared that he might inject something in your hearts, or he said “evil” (instead of something).  

كَانَ رَسُولُ اللَّهِ ﷺ مُعْتَكِفًا فَأَتَيْتُهُ أَزُورُهُ لَيْلاً فَحَدَّثْتُهُ وَقُمْتُ فَانْقَلَبْتُ فَقَامَ مَعِي لِيَقْلِبَنِي وَكَانَ مَسْكَنُهَا فِي دَارِ أُسَامَةَ بْنِ زَيْدٍ فَمَرَّ رَجُلاَنِ مِنَ الأَنْصَارِ فَلَمَّا رَأَيَا النَّبِيَّ ﷺ أَسْرَعَا فَقَالَ النَّبِيُّ ﷺ عَلَى رِسْلِكُمَا إِنَّهَا صَفِيَّةُ بِنْتُ حُيَىٍّ قَالاَ سُبْحَانَ اللَّهِ يَا رَسُولَ اللَّهِ قَالَ إِنَّ الشَّيْطَانَ يَجْرِي مِنَ الإِنْسَانِ مَجْرَى الدَّمِ فَخَشِيتُ أَنْ يَقْذِفَ فِي قُلُوبِكُمَا شَيْئًا أَوْ قَالَ شَرًّا