The Book of Prayers - Sahih Muslim 402b

"Then he may choose any supplication which pleases him." This narration from Sahih Muslim establishes the permissibility of personal supplication (du'a) after the obligatory prayers. The classical scholars explain that this refers to the period following the completion of the prescribed prayer, before the final taslim (salutation).

Imam al-Nawawi comments in his Sharh Sahih Muslim that this hadith demonstrates the flexibility granted to the worshipper in selecting personal invocations. The phrase "which pleases him" indicates that one may choose from established prophetic supplications or formulate one's own sincere requests in any language, provided the content conforms to Islamic principles.

This ruling reflects the mercy of Islamic law, allowing believers to communicate with their Creator using words that resonate with their hearts and circumstances, while maintaining the proper etiquette of supplication as taught by the Prophet Muhammad (peace be upon him).