Sunan Abi Dawud 834
The above-mention tradition has also been transmitted through a different chain of narrators by Humaid, but he did not mention the word “Supererogatory prayer” This version has:
Al-Hasan (al-Basri) would recite fatihat al-kitab in the noon and afternoon prayers while he led in prayer or he was behind the imam and would glorify Allah, and would repeatedly say: “Allah is most great” and “ There is no god but Allah” (i.e takbir and tahlil) equal to the amount one recites al-Qaf (Surah 50) and al-Dhariyat(surah 51).
حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا حَمَّادٌ، عَنْ حُمَيْدٍ، مِثْلَهُ لَمْ يَذْكُرِ التَّطَوُّعَ قَالَ كَانَ الْحَسَنُ يَقْرَأُ فِي الظُّهْرِ وَالْعَصْرِ إِمَامًا أَوْ خَلْفَ إِمَامٍ بِفَاتِحَةِ الْكِتَابِ وَيُسَبِّحُ وَيُكَبِّرُ وَيُهَلِّلُ قَدْرَ ق وَالذَّارِيَاتِ ‏.‏