There's a lot of debate on this, and honestly, I probably am less stringent about this than others in the breastfeeding community. However, the recommendation is to not introduce artificial nipples - including pacifiers - until breastfeeding is well-established. The main concern is that a mother will miss her child's hunger cues by just giving them a pacifier rather than feeding on demand. In my experience, I have given a pacifier from the beginning and had no issues. But the "official" response would be to wait for a few weeks. Here is a great article about breastfeeding and pacifiers that you might want to read.