✅ Answer:

1⃣قال الصادق علیه السلام فی حدیث... فَإِنَّ صَلَاةَ الزِّیَارَةِ ثَمَانٍ أَوْ سِتٌّ أَوْ أَرْبَعٌ أَوْ رَکْعَتَانِ وَ أَفْضَلُهَا ثَمَانٍ....

Imam Sadiq (AS) said in a hadith:

Indeed, the Ziyarat prayer is eight rak'ahs, six rak'ahs, four rak'ahs, or two rak'ahs, and the best of them is eight rak'ahs...

2⃣ Important Note:

قال الصادق علیه السلام فی حدیث :وَ إِنْ شِئْتَ صَلَّيْتَ خَلْفَ الْقَبْرِ وَ عِنْدَ رَأْسِهِ أَفْضَلُ فَإِذَا فَرَغْتَ فَصَلِّ مَا أَحْبَبْتَ إِلَّا أَنَّ الرَّكْعَتَيْنِ رَكْعَتَيِ الزِّيَارَةِ لَا بُدَّ مِنْهُمَا عِنْدَ كُلِّ قَبْرٍ

📚 Mustadrak, Vol. 10, Page 327

Translation:

Imam Sadiq (AS) said in a hadith after mentioning the manner of Ziyarat: ... If you wish, perform the Ziyarat prayer behind the grave, and near the head of the Imam is preferable. Once you finish the Ziyarat, you may pray as much as you like, except that two rak'ahs of Ziyarat prayer at each Imam’s grave are obligatory and unavoidable.

3⃣ One of the blessings of the Ziyarat prayer:

عَلِیُّ بْنُ مُوسَی بْنِ طَاوُسٍ فِی مِصْبَاحِ الزَّائِرِ عَنِ الصَّادِقِ فِی حَدِیثٍ أَنَّ مَنْ زَارَ إِمَاماً مُفْتَرَضَ الطَّاعَةِ بَعْدَ وَفَاتِهِ وَ صَلَّی عِنْدَهُ أَرْبَعَ رَکَعَاتٍ کُتِبَتْ لَهُ حَجَّةٌ وَ عُمْرَةٌ

📚 Mustadrak, Vol. 10, Page 184

Translation:

It is narrated in a hadith from Imam Sadiq (AS) that he said: Whoever visits an Imam, who is divinely appointed to be obeyed, after his passing and performs four rak'ahs of Ziyarat prayer near him, it will be recorded for him as one Hajj and one Umrah.

4⃣ Note:

مُحَمَّدُ بْنُ إِدْرِیسَ فِی آخِرِ السَّرَائِرِ نَقْلًا مِنْ کِتَابِ حَرِیزِ بْنِ عَبْدِ اللَّهِ عَنْ أَبِی بَصِیرٍ قَالَ قَالَ أَبُو جَعْفَرٍ فِی حَدِیثٍ وَ افْصِلْ بَیْنَ کُلِّ رَکْعَتَیْنِ مِنْ نَوَافِلِکَ بِالتَّسْلِیمِ

📚 Wasa'il al-Shia, Vol. 4, Page 63

Translation:

Imam Baqir (AS) said in a hadith: Separate every two rak'ahs of your voluntary prayers with a greeting (salam).