Isaiah 2:4, from the vision of the mountain of the LORD that opens the book. The same prophecy appears almost word for word in Micah 4:3, which is one of the clearest cases in the Tanakh of two prophets carrying the same oracle.
לְאִתִּים (le-i-tim) and לְמַזְמֵרוֹת (le-maz-me-rot) are not generic farm implements; the first is the iron share of a plough, the second the curved blade used to prune vines. The image is precise: the metal of war is not thrown away, it is reforged into the two tools that feed people. That is a stronger claim than disarmament.
Sung at school assemblies, at memorial ceremonies, and at every gathering that wants to end on something other than a speech. There is no single canonical melody — several rounds circulate and they are all called by the same first three words, so if two people start it in different tunes, neither of them is wrong.