Which is better: to limit oneself in prostration to the supplications authentically reported from the Prophet, may Allah bless him and grant him peace, or to supplicate with whatever pleases me, taking advantage of the servant's proximity to his Lord in this state?

It is best to recite the supplications reported from the Prophet, peace and blessings be upon him, during prostration, and it is good to add to them. It is permissible to recite some of the reported supplications and other supplications, based on the Prophet's saying, peace and blessings be upon him: "As for bowing, glorify the Lord, the Exalted and Most High, therein, and as for prostration, strive in supplication, for it is most likely that you will be answered."