In one narration the words are: I asked Sayyiduna Abu Umamah (may Allah be pleased with him) about the additional (prayer), and he said: It was additional for the Prophet (peace and blessings be upon him), and for you it is a source of merit (that is, it is recommended). Ahmad recorded all of these reports with two chains; one chain contains a narrator, Shahr, and the other contains a narrator, Abu Ghalib. Both have been declared trustworthy, and there is a weakness in both of them that is not harmful.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11132