Bismillah Arrahman Arraheem 

The last day of Zilhajj  is the last day in the Arabic calendar. Sayyid Ibn Tawoos in his book of Iqaab al-A'maal, says it is recommended to offer a two unit prayer on this day reciting Surah Fatihah once, and repeating each of Surah Tawheed and Ayat al Kursi ten times. After the salat, it is recommended to say the following

اَللَّهُمَّ مَا عَمِلْتُ فِي هٰذِهِ ٱلسَّنَةِ

Allahumma maa alimtu fi hadhihi sanah

مِنْ عَمَلٍ نَهَيْتَنِي عَنْهُ وَلَمْ تَرْضَهُ

min amalin nahaytani anhu wa lam tardhah

وَنَسِيتُهُ وَلَمْ تَنْسَهُ

Wa naseetuhu wa lam tansah

وَدَعَوْتَنِي إِلَىٰ ٱلتَّوْبَةِ بَعْدَ ٱجْتِرَائِي عَلَيْكَ

wa da’awtani ila tawbati ba’ada ijtira’yi alaika

اَللَّهُمَّ فَإِنِّي اسْتَغْفِرُكَ مِنْهُ فَٱغْفِرْ لِي

Allahumma fa inni astaghfiruka minhu faghfirli

وَمَا عَمِلْتُ مِنْ عَمَلٍ يُقَرِّبُنِي إِلَيْكَ

wa maa amiltu min amalin yuqarribuni ilayka

فَٱقْبَلْهُ مِنِّي وَلاَ تَقْطَعْ رَجَائِي مِنْكَ يَا كَرِيمُ

faqbalhu minni wa laa taqta' rajaa'i minka ya kareem

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.

Reference