✅ Answer: Please pay attention to the following narration:

1 مُحَمَّدُ بْنُ یَحْیَی عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عُثْمَانَ بْنِ عِیسَی عَنْ سَمَاعَةَ قَالَ: سَأَلْتُ أَبَا عَبْدِ اللَّهِ عَنْ غُسْلِ الْجُمُعَةِ فَقَالَ وَاجِبٌ فِی السَّفَرِ وَ الْحَضَرِ إِلَّا أَنَّهُ رُخِّصَ لِلنِّسَاءِ فِی السَّفَرِ لِقِلَّةِ الْمَاءِ وَ قَالَ غُسْلُ الْجَنَابَةِ وَاجِبٌ وَ غُسْلُ الْحَائِضِ إِذَا طَهُرَتْ وَاجِبٌ وَ غُسْلُ الْمُسْتَحَاضَةِ وَاجِبٌ إِذَا احْتَشَتْ بِالْکُرْسُفِ فَجَازَ الدَّمُ الْکُرْسُفَ فَعَلَیْهَا الْغُسْلُ لِکُلِّ صَلَاتَیْنِ وَ لِلْفَجْرِ غُسْلٌ وَ إِنْ لَمْ یَجُزِ الدَّمُ الْکُرْسُفَ فَعَلَیْهَا الْغُسْلُ کُلَّ یَوْمٍ مَرَّةً وَ الْوُضُوءُ لِکُلِّ صَلَاةٍ وَ غُسْلُ النُّفَسَاءِ وَاجِبٌ وَ غُسْلُ الْمَوْلُودِ وَاجِبٌ وَ غُسْلُ الْمَیِّتِ وَاجِبٌ وَ غُسْلُ الزِّیَارَةِ وَاجِبٌ وَ غُسْلُ دُخُولِ الْبَیْتِ وَاجِبٌ وَ غُسْلُ الِاسْتِسْقَاءِ وَاجِبٌ وَ غُسْلُ أَوَّلِ لَیْلَةٍ مِنْ شَهْرِ رَمَضَانَ یُسْتَحَبُّ وَ غُسْلُ لَیْلَةِ إِحْدَی وَ عِشْرِینَ وَ غُسْلُ لَیْلَةِ ثَلَاثٍ وَ عِشْرِینَ سُنَّةٌ لَا تَتْرُکْهَا فَإِنَّهُ یُرْجَی فِی إِحْدَاهُنَ لَیْلَةُ الْقَدْرِ وَ غُسْلُ یَوْمِ الْفِطْرِ وَ غُسْلُ یَوْمِ الْأَضْحَی سُنَّةٌ لَا أُحِبُّ تَرْکَهَا وَ غُسْلُ الِاسْتِخَارَةِ یُسْتَحَبُ...

📚 Al-Kafi Vol. 3, p. 40

Sama'ah said: I asked Imam Sadiq (peace be upon him) about the ghusl of Friday; the Imam said: 'It is obligatory whether one is traveling or at home, except that when traveling, there is a dispensation for women when there is a shortage of water.' He said: 'And the ghusl of janaba is obligatory, and the ghusl of a menstruating woman when she becomes clean is obligatory, and the ghusl of a woman with istiḥaḍa (irregular bleeding) is obligatory; when she places cotton in herself and the blood goes beyond the cotton, it is her responsibility to perform ghusl for every two prayers (i.e., one ghusl for the dhuhr and asr prayers and one ghusl for the maghrib and isha prayers) and also perform one ghusl for the morning prayer, and if the blood does not go beyond the cotton, it is her responsibility to perform one ghusl a day and perform wudu' for every prayer, and the ghusl of nifas (i.e., a woman who has seen blood after childbirth) is obligatory, and the ghusl for a newborn is obligatory, and the ghusl for a deceased person is obligatory, and the ghusl for visiting (the House of Allah) is obligatory, and the ghusl for entering the House of Allah is obligatory, and the ghusl for istisqa' (i.e., the prayer for rain) is obligatory, and the ghusl of the first night of the month of Ramadan is recommended, and the ghusl of the twenty-first night and the twenty-third night are a tradition that you do not abandon, because in one of them is the hope of the Night of Qadr, and the ghusl of the day of Eid al-Fitr and the day of Eid al-Adha are a tradition that I do not like to be abandoned, and the ghusl of istikhara is recommended!'

✅ Based on the above narration and others, one of the ghusls mentioned in the narrations is the ghusl of istikhara, so when a person wants to perform istikhara using one of the methods mentioned in the narrations, he first performs ghusl and then performs the desired istikhara. Of course, this ghusl is not among the obligatory ghusls and is one of the recommended ghusls.

اللَّهُمَّ صَلِّ عَلَی مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ عَجِّلْ لِوَلِیِّکَ الْفَرَجَ وَ الْعَافِیَةَ وَ النَّصْرَ