Putting Hand Under Armpit
Scholars have said that whoever dreams of putting their hand under their armpit and then pulling it out with light, they will gain knowledge if they are worthy, or profit if they are a merchant. If the hand comes out with fire, they will gain strength, dominance, and honor in their endeavors. If it comes out with water, it signifies wealth. An extra hand (beyond the natural two) indicates an increase in power and strength, or a child, the return of an absent person, or the birth of a brother.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam