It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "The believer is not one who taunts, nor one who curses, nor one who is obscene, nor one who is vulgar." This hadith is sahih on the condition of the two Shaykhs; they used all of these narrators as evidence, yet they did not narrate it. The most that can be said about it is that it is not found with the (general) students of al-A'mash, whereas Isra'il bin Yunus al-Sabi'i is the senior-most and leader of his students, and he shares many of al-A'mash's teachers with him, so his being alone (in narrating) this hadith is not grounds for rejecting it. This hadith also has another corroborating narration (shahid) on the condition of both of them.