Answer
(Fatwa: 1154/1154=M/1429)
If the bad thought come in your mind automatically without your will, then it is not bad, rather it is bad to invite such thoughts or accommodate them. While outside salah, if the bad thoughts come you should recite:
أعوذ باللہ من الشیطان الرجیم
In leisure time, instead of sitting idle you should engage yourself in reciting Quran and Zikr. Also, you should keep on reciting the below duas:
أللھم أعني علی ذکرک و شکرک و حسن عبادتک
أللھم اجعل وساوس قلبي خشیتک وذکرک واجعل ھمتي و ھواي فیما تحب و ترضی رب أعوذبک من ھمزات الشیاطین وأعوذبک رب أن یحضرون
Likewise, recite Surah Al-Falaq, Surah Al-Naas and Ayatul Kursi etc and blow on your body in the morning and evening. If possible, you should get bai?ah with any pious and follower of Sunnah sheikh.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband