What is the Hadith about Janazah prayer ( for an absent person) and within how many days we have to conduct that prayer?

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
The Hadith which proves the offering of funeral prayer for an absent person is a sound one reported by Abu Hurayrah that "The Prophet (Sallallahu Alaihi wa Sallam) informed his companions about the death of Negus (Najashi), the king of Abyssinia, the day that he passed away. And then the Prophet led them to the prayer ground where he lined them up and offered funeral prayer for him with four Takbirs". [Reported by Imams Bukhari and Muslim]
The time for offering funeral prayer for an absent person should be within one month after his death according to the most correct opinion. This rule is deduced from the Mursal Hadith that the Prophet performed funeral prayer on a grave of a woman one month after her death as reported from Sayeed Ibn al-Musayyab that 'Saad Bin Ubadh's mother died while the Prophet was absent. When he came to Madinah one month later he offered the funeral prayer on her grave'. [Tirmizi]
Allah knows best.