The last* day of Dhū al-Ḥijjah is the last day in the Arabic calendar. According to some narrations mentioned by Sayyid Ibn Tawus in his book of Iqbal al-A’mal, it is recommended to offer a two unit prayer on this day reciting Surah al-Fatehah once, and repeating each of Surah al-Tawḥīd and Ayah al-Kursi ten times. After accomplishment, it is recommended to say the following supplication:
اَللّٰهُمَّ مَا عَمِلْتُ فِي هَذِهِ السَّنَةِ مِنْ عَمَلٍ نَهَيْتَنِي عَنْهُ وَ لَمْ تَرْضَهُ وَ نَسِيتُهُ وَ لَمْ تَنْسَهُ وَ دَعَوْتَنِي اِلَى التَّوْبَةِ بَعْدَ اجْتِرَائِي عَلَيْكَ اَللّٰهُمَّ فَاِنِّي اَسْتَغْفِرُكَ مِنْهُ فَاغْفِرْ لِي وَ مَا عَمِلْتُ مِنْ عَمَلٍ يُقَرِّبُنِي اِلَيْكَ فَاقْبَلْهُ مِنِّي وَ لا تَقْطَعْ رَجَائِي مِنْكَ يَا كَرِيمُ
If these statements are said, Satan will say, “Woe to me! All the efforts that I have exerted throughout this year for misleading this person have been failed by the utterance of these statements.” Besides, one who says these words will be testified by the year that he sealed it in a good way.
*29th or 30th depending on the length of the month