Khalaf bin Hafs narrated about Sayyiduna Anas (may Allah be pleased with him): We were taken to Abd al-Malik in al-Sham, and we were forty men from the Ansar; the purpose was that he should fix a stipend for us. When he returned and we were at Fajj al-Naqah, he led us in the Zuhr prayer with two rak'ahs, then he went into his tent. The people stood up and added two more rak'ahs to their two rak'ahs. So Sayyiduna Anas (may Allah be pleased with him) said: "May Allah Almighty make the faces of these people ugly! By Allah, they have neither followed the Sunnah nor accepted the concession. I bear witness that I heard the Prophet (peace and blessings be upon him) saying: 'Some people will go to extremes in the religion, and they will pass out of the religion just as an arrow passes through the target.'"
Ahmad recorded it; I have not found anyone who wrote a biography of Khalaf bin Hafs.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2941