Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: The Prophet (peace and blessings be upon him) prayed five rak'ahs in the Asr prayer, so he performed the two prostrations of error (i.e. the prostrations of forgetfulness) while he was sitting.
Al-Bazzar and al-Tabarani in al-Mu'jam al-Kabir and al-Mu'jam al-Awsat recorded it; its chain contains a narrator, Sa'id bin Bashir, who is thiqah (trustworthy), but his memory became confused (ikhtilat).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2918