It is narrated from Hazrat Abu Umamah (may Allah be pleased with him) regarding the interpretation of the Quranic verse "Nafilatan laka" that the observance of voluntary prayers (nawafil) was specific to the Prophet Muhammad (peace and blessings be upon him).
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 22210
Hadith Gradingحکم دارالسلام:إسناده ضعيف لضعف شهر ، وقد تابعه راو ضعيف أيضا