Beer e Shifa.
Well of Shifa near Badr on the way Madinah or in between Madinah or Badr. This well had poisoness water, whoever drinks this well water including animals, soon they die. Sahabah requested Prophet ﷺ to have water as they are feeing thirsty. It was converted into sweet water Well after Muhammad ﷺ sped his saliva in the well.