...فَصَلَّ رَكْعَتَيْنِ وَ اسْتَخِرِ اللهُ مَرّةٍ وَ مَرّةٍ ثُمَّ انْظُرْ أَحْزَمَ الأَمْرَيْنِ لَكَ فَافْعَلْهُ الْخِيَرَةَ فِيهِ إِنْ شٰاءَ اللهُ
al‑Imam al‑Sadiq (as) said: "...recite a two Rak'at Salat and then ask the best from Allah one hundred and one times and see which of the two ways (either to perform that act or not perform it) is stronger (in your heart) and act accordingly, since whatever is best for you is in that, Insha‑Allah. "10
The only person who will be able to make use of this method of seeking what is the best is the one whose heart has been purified of the various types of whispers of Shaitan and whose heart has not become polluted with sins. Such a heart is one that still has the desire and capability of receiving the heavenly inspiration of Allah.
10. al‑Kafi, Volume 3, Page 472 / Tahdhib al‑Ahkam, Volume 3, Page 181, Hadith 411 / Wasa'il ash‑Shi'a Volume 8, Page 65, Hadith 10098