Anas (RA) said that he heard the Prophet (SAW) say: "That I sit with people remembering Almighty Allah from the morning (Fajr) prayer until sunrise is more beloved to me than freeing four slaves from among the Children of Isma'il. That I sit with people remembering Allah from the afternoon ('Asr) prayer until the sun sets is more beloved to me than freeing four slaves from among the Children of Isma'il."

Reference: Hasan (Albani). Abu Dawud: 3667