It is narrated on the authority of Hazrat Abu Saeed Khudri (may Allah be pleased with him) in a marfu’ form that when a person has doubt in his prayer and does not remember whether he has performed more or fewer rak‘ahs, then he should perform two prostrations of forgetfulness while sitting.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 11383
Hadith Gradingحکم دارالسلام:حديث صحيح لغيره، وهذا إسناد حسن