Not circumcising before the eighth day: Shabbat 132a
The proper date of circumcision for a child born at sunset between two days: Shabbat 137a
Delaying circumcision in order to fulfill the mitzvah of meit mitzvah - burying a body which has no buriers: Berachot 19b; Megillah 3b
Delaying for a sick child: Shabbat 137a
How long one must wait to circumcise after a child's fever breaks: Shabbat 137a
Cures for an infant who is too sick for circumcision: Shabbat 134a
Signs that the infant isn't ready: Shabbat 134a