I saw him play. (Passive)

Explanation: There are two basic rules for converting sentences from Active Voice into Passive Voice, which are common for all tenses.
1) The places of subject and object will be interchanged in the sentence.
2) Only 3rd form of the verb or Past Participle (e.g. written) will be used as a main verb in Passive Voice.

Need, see, bid, dare, make, hear, feel, let, know, behold, watch প্রভৃতি verb গুলোর পর Active Voice-এ to উহ্য থাকে।
তবে passive করার সময় তাদের পরে to বসে।