In one narration the words are: She narrates: The Prophet (peace and blessings be upon him) came to me on the third day after the martyrdom of Sayyiduna Ja'far (may Allah be pleased with him) and said: "Do not mourn after this day of yours."
Ahmad recorded all of these narrations, and al-Tabarani recorded some of them in al-Mu'jam al-Kabir. The narrators of Ahmad are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 4044