It is narrated from Asma' bint Umays (may Allah be pleased with her): When Ja'far (may Allah be pleased with him) was martyred, the Messenger of Allah (peace and blessings be upon him) instructed me: "Observe mourning for three days, then do as you wish."
Abdullah (bin Shaddad)'s hearing from Asma' is not established; it has also been said in it 'from Asma'', so it is mursal. Muhammad bin Talhah is not strong, and the hadiths before it are more firmly established, so following them is more appropriate.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15523