What is the biblical basis for women, particularly mothers, working outside of the home? I'm wondering about the sinfulness of women, particularly mothers, working outside the home.  Perhaps 1 Timothy 5:8 could be understood to mean that only the husband is to provide for the family:

Anyone who does not provide for their relatives, and especially for their own household, has denied the faith and is worse than an unbeliever.
1 Timothy 5:8 NIV

What is the biblical basis for a woman, particularly a mother, working outside the home?
Proverbs 31 is considered (by many) to be the model of what a godly woman should be.  In this chapter, we see that this woman is actually quite industrious:

10An excellent wife who can find?  She is far more precious than
jewels. 11The heart of her husband trusts in her, and he will have no
lack of gain. 12She does him good, and not harm, all the days of her
life.
13She seeks wool and flax, and works with willing hands.
14She is like the ships of the merchant; she brings her food from afar.
15She rises while it is yet night and provides food for her household
and portions for her maidens. 16She considers a field and buys it;
with the fruit of her hands she plants a vineyard. 17She dresses
herself with strength and makes her arms strong. 18She perceives
that her merchandise is profitable.  Her lamp does not go out at
night. 19She puts her hands to the distaff, and her hands hold the
spindle.
20She opens her hand to the poor and reaches out her hands
to the needy. 21She is not afraid of snow for her household, for all
her household are clothed in scarlet. 22She makes bed coverings for
herself; her clothing is fine linen and purple. 23Her husband is
known in the gates when he sits among the elders of the land. 24She
makes linen garments and sells them; she delivers sashes to the
merchant.
25Strength and dignity are her clothing, and she laughs at
the time to come. 26She opens her mouth with wisdom, and the teaching
of kindness is on her tongue. 27She looks well to the ways of her
household and does not eat the bread of idleness.
28Her children rise up and call her blessed; her husband also, and he praises her:
29&quot;Many women have done excellently, but you surpass them all.&quot;
30Charm is deceitful, and beauty is vain, but a woman who fears
the LORD is to be praised. 31Give her of the fruit of her hands,
and let her works praise her in the gates.
Proverbs 31:10-31 ESV

So, no, in no way does the Bible say it is sinful for a woman to work outside the home.
That being said, men and women are still different, and masculinity is different from femininity.
Most Christian families that I know of where the woman does not work outside the home have made that choice because of their own priorities.  They have decided that freeing up the wife or mother to focus more effort on caring for the family and being active in the lives of their children is more important than the extra money and career success that the woman could otherwise achieve in the workplace.
It goes both ways, though.  I believe that both the man who has a career and the woman should value the family more than career advancement and prestige.  For the man, that may mean not getting that next promotion that requires more hours, so that he can spend more time caring for his wife and children.