Sayyid Ibn Tawus and Shaykh al-Saduq have both narrated the following on the authority of Jabir ibn ‘Abdullah al-Ansari:
I visited the Messenger of Allah (a.s.) on the last Friday of Ramaḍān. As he saw me, he said: O Jabir, this is the last Friday of Ramaḍān. You should thus bid farewell to it by saying the following:
اَللّٰهُمَّ لَا تَجْعَلْهُ آخِرَ الْعَهْدِ مِنْ صِيَامِنَا اِيَّاهُ
allahumma la taj`alhu akhira al`ahdi min siyamina iyyahu
O Allah: (please) do not make it the last of our fasting in this month;
فَاِنْ جَعَلْتَهُ فَاجْعَلْنِي مَرْحُوْمًا وَ لَا تَجْعَلْنِي مَحْرُوْمًا
fa-in ja`altahu faj`alny marhuman wa la taj`alny mahruman
but if You decide so, then (please) make me enjoy (Your) mercy and do not make me deprived (of it).
Verily, whoever says this supplication will win one of the two good things; either attaining the next Ramaḍān or having the forgiveness and mercy of Almighty Allah.