Is the hadith narrated by Anas, may Allah be pleased with him: "There are no two servants who love each other for the sake of Allah who meet each other and shake hands and invoke blessings upon the Prophet, peace and blessings of Allah be upon him, except that they do not part until their sins, past and future, are forgiven for them," authentic? And if it is weak, can it be acted upon?

This hadith (definition) was narrated by Ibn Al-Sunni from Anas, by Abu Ya'la in his Musnad, and by Ibn Hibban in Al-Dhu'afaa' (The Weak Narrators). It was reported in Abu Dawud and Ibn Hibban with authentic and good chains of narration, but without the addition of sending blessings upon the Prophet or forgiveness of past sins.

It is permissible to act upon it in matters concerning the virtues of deeds, even if it is weak, according to those who permit it, out of hope for reward, while not believing in its definitive authenticity from the Prophet, peace and blessings be upon him. Rather, one acts upon it as a precautionary measure.