(a) This hadith is also transmitted through another chain, in which it states that the Prophet (peace and blessings be upon him) led them in prayer and forgot; then he (peace and blessings be upon him) performed two prostrations, after which he recited the tashahhud and then gave the salam.
(b) Muhammad states: I was informed via Imran (may Allah be pleased with him) that he mentioned the salam and did not mention the tashahhud; and in the narration of Hushaym the tashahhud is mentioned before the two prostrations.
Ash'ath al-Humrani is alone in narrating this. Shu'bah, Wuhayb, Ibn Ulayyah, al-Thaqafi, Hushaym, Hammad bin Zayd, Yazid bin Zuray' and others narrated it from Khalid al-Hadhdha, and none of them mentioned what Ash'ath mentioned from Muhammad from him; this indicates Ash'ath's error in what he narrated.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3897