إِنَّ يَسِيرَ الرِّيَاءِ شِرْكٌ
Translation: Even a small amount of showing off in worship is a form of associating others with Allah.
Source: ابن ماجه
Showing off arises when praise from people, rather than Allah’s pleasure, becomes the goal of worship. It can corrupt the inner purpose of an outwardly good deed. Even a seemingly small element of display merits careful self-examination.
يَسِيرَ الرِّيَاءِ means “a small amount of showing off”; its two words form an iḍāfah (possessive) construction. شِرْكٌ is the predicate, expressing the seriousness of the warning. The report is not a license to judge the hidden faith of particular people.
Sincerity means keeping Allah’s pleasure as the main purpose whether or not anyone praises the deed.