Is a servant's supplication to his Lord for sustenance and money invalid?

There is no basis for the saying that supplicating for oneself, wealth, or family is invalid. Supplicating for permissible worldly pleasures outside of prayer is undoubtedly permissible.

Scholars have differed on the permissibility of supplicating within prayer for worldly pleasures not mentioned in the transmitted supplications. Some, like the Hanafis and Hanbalis, prohibited it, while the Malikis and Shafi'is permitted it, citing the hadith: "Then let him choose whatever supplication he wishes."

The most sound opinion is permissibility. A worshipper can supplicate for whatever they wish, be it related to worldly matters or the Hereafter. However, if one desires to be cautious and avoid the difference of opinion, they may make supplications for worldly pleasures outside of prayer.