Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) states regarding this saying of Allah Almighty (the Exalted says): "They ask you about fighting in the sacred month. Say: fighting in it is a great (sin)." The narrator says: The Prophet (peace and blessings be upon him) had sent Abdullah bin so-and-so on an expedition, and at the place called Batn Nakhlah those people encountered Amr bin al-Hadrami. The narrator says: after this he mentioned the long hadith.
Al-Bazzar recorded it. Its chain contains Abu Sa'id al-Baqqal, and he is da'if (weak).