Is it better to supplicate after the salām or before it in the supererogatory and obligatory prayers?

Supplication (Du'a) is permissible in prayer both before and after the salutations (taslim). There is abundant evidence that the Prophet (peace be upon him) consistently made supplications before the salutations, as his supplications in prayer were before exiting it, such as the supplication: "O Allah, I seek refuge in You from the torment of Hellfire..." and his saying to his companions: "Then let him choose of the supplication what he likes most."

Supplication is not restricted to after the salutations only; rather, it includes both before and after. Supplication within prayer is more emphasized and potent than after exiting it. The Prophet (peace be upon him) taught Abu Bakr As-Siddiq a supplication to recite in his prayer.

The permissibility of supplication before and after the salutations encompasses both obligatory (fard) and voluntary (nafl) prayers. Supplication after an obligatory prayer is better than after a voluntary one. Aisha (may Allah be pleased with her) narrated the Prophet's (peace be upon him) supplication during his night prayer, and that it was before exiting the prayer.

Thus, supplication in prayer is permissible both before and after the salutations. It is preferable to make it before the salutations due to the abundance of texts indicating the Prophet's (peace be upon him) consistent practice of this, and this applies to both obligatory and voluntary prayers.