從 = cóng = to follow; to come after; from [hsk2, as 从]
⾨ = mén = gate [hsk2 as 门]
⼊ = rù = enter [not in hsk?]
者 = zhě = that which (referring to preceding phrase) [hsk3]
不 = bù = not [hsk1]
是 = shì = this; is [hsk1]
家 = jiā = family [hsl1]
珍 = zhēn = treasure; precious thing; rare; valuable [hsk5]
1. 従 is a variant form of 從 (specifically Shinjitai, “new character form”, used in Japan)
2. The simplified form of this Zen saying is quite common: 从门入者不是家珍. If you do a google search on the traditional form in quotes you will get zero hits. But if you do a google search using the simplified form, you’ll get almost 10,000 hits.
Source: Kusumoto Bunyū’s (久須本⽂雄) 1982 book Zengo Nyūmon (禅語⼊⾨, An Introduction to Zen Words and Phrases, Tokyo: Daihōrin-kaku Co. Ltd.
URL (English translation by Michael D. Ruymar, but this translation still provides lots of the original Chinese): https://terebess.hu/zen/Zengo.pdf
And also check this out (all in Chinese): http://fodizi.net/fojiaogushi/3278.html