a source [of bliss] whereof God's servants shall drink, seeing it flow in a flow abundant.

A Fountain where the Devotees of God do drink, making it flow in unstinted abundance.

A spring wherefrom the slaves of Allah drink, making it gush forth abundantly,

A fountain from which the servants of Allah drink, making it flow in abundance.

A spring of which the [righteous] servants of Allah will drink; they will make it gush forth in force [and abundance].