What is the meaning of: "Two nights passed and four remained," the well of Arees, and what is the well of Arees?

What you inquired about is part of the speech of Zayd ibn Kharijah al-Ansari, who is narrated to have spoken after his death. This story is mentioned in books of Hadith (definition) and history, including the narration by al-Tabarani, which states that he spoke after his death, addressing those present and praising the Prophet Muhammad, peace and blessings be upon him, then Abu Bakr, Umar, and Uthman.

Al-Hafiz al-Dhahabi, Ibn Kathir, and others commented on this, explaining that his statement about Uthman, "Two have passed and four remain," refers to the incident of the Prophet’s ring falling into the well of Aris six years into Uthman’s caliphate, and the subsequent change in affairs and the emergence of tribulations.

Al-Bukhari referred to Zayd ibn Kharijah as one of the martyrs of Badr and as the one who spoke after death. Al-Bayhaqi mentioned that narrations of speaking after death have been reported from a group with authentic chains of transmission. Ibn Abd al-Barr affirmed that Zayd fainted and his soul ascended, then returned, and he spoke about the Rightly Guided Caliphs, and then died immediately.