Why do saline hydrides release hydrogen gas when mixed with water?

Saline (or ionic) hydrides release hydrogen gas when mixed with water because they contain the hydride anion ($H^{-}$), which acts as a strong base.1

When these compounds come into contact with water, the hydride ion reacts instantly and quantitatively with the hydrogen ion ($H^{+}$) provided by the water molecules. This chemical reaction is represented by the following equation:

$$H^{-}+H_{2}O\to H_2+O{H}^{-}$$

In this process, the hydride ion accepts a proton from the water, resulting in the formation of hydrogen gas ($H_2$) and the hydroxide ion ($O{H}^{-}$) in the solution. Because this reaction is vigorous and produces large volumes of hydrogen, saline hydrides are frequently utilized as portable sources of hydrogen gas.1