It is narrated from Sayyiduna Sa'd bin Zayd al-Ashhali (may Allah be pleased with him) that he gave the Prophet (peace and blessings be upon him) a sword from Najran as a gift, or a sword from Najran was gifted to the Prophet (peace and blessings be upon him). When it reached him, he gave it to Sayyiduna Muhammad bin Maslamah (may Allah be pleased with him) and said: "Fight with this in the path of Allah. When the necks of the people go different ways (that is, when tribulation breaks out), strike it against a rock and break it, then go into your house and be like a saddle-cloth thrown on the ground, until a sinning (wrongdoing) hand kills you or the appointed death comes to you."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5405