It was quoted to me years ago from mishnah brura, but I cannot find it there now. I am familiar with the line in Avot "no better guard for wisdom than silence" // that is not exact. Guidance and references are appreciated. (And I acknowledge that the friend who told me of this wisdom may have him...

I have two related questions: Can I find Nechama Lebowitz books online anywhere for free? I often see her books titled either with or without the word new. For example "Studies in Vayikra" or "New Studies in Vayikra". Are these separate books or just different editions?