Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: My place of standing was directly behind the Prophet (peace and blessings be upon him), between his two shoulders. When he finished the prayer with the salam, he recited this supplication: 'Allahummaj'al khayra 'umri akhirahu, Allahummaj'al khawatima 'amali ridwanaka, Allahummaj'al khiyara ayyami yawma alqak' "O Allah, make the best part of my life its last part; make the conclusion of my deeds one of Your good pleasure; and O Allah, make the best of my days the day on which I come before You."
Al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains Abu Malik al-Nakha'i, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16974