Is it permissible to perform the Istikhara supplication without prayer, and is one Istikhara prayer sufficient for all matters of life, or is it better to perform Istikhara for each matter separately?

The origin and Sunnah regarding Istikhara is through prayer and supplication in every matter of concern to a Muslim, based on Jabir's statement: "The Messenger of Allah, peace and blessings be upon him, used to teach us Istikhara in all matters." It is permissible to suffice with the Istikhara supplication if prayer is difficult, especially during times of impediments such as menstruation or preoccupation. It is best that Istikhara be performed in the manner the Prophet, peace and blessings be upon him, taught his Companions, which is two voluntary rak'ahs followed by the well-known supplication that begins with "O Allah, I seek Your guidance by Your knowledge."