It is narrated from Sayyiduna Abdullah bin Ja'far (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is in doubt about his prayer, let him perform two prostrations after giving the salam."
There is no harm in this chain, except that the hadith of Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) is more authentic in its chain than it, and with it are the hadiths of Sayyiduna Abd al-Rahman bin Awf and Sayyiduna Abu Hurayrah (may Allah be pleased with them both), as we shall mention. Wallahu a'lam (And Allah knows best).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3821