Skanda Purana (स्कन्दपुराण) is the largest Mahapurana, among eighteen Hindu religious texts. The text contains over 81,000 verses, named after Skanda, son of Shiva and Parvati, who is also known as Kartikeya and Murugan. Since this purana is narrated by Lord Skanda himself, therefore it is called as Skanda Purana.
In this purana under the Maheshvera Khanda – Kumarika Khanda – chapter 23, verse 46, it is mentioned that a daughter is equal to ten sons –
दशपुत्रसमा कन्या दशपुत्रान्प्रवर्द्धयन्।
यत्फलं लभते मर्त्यस्तल्लभ्यं कन्ययैकया॥
One daughter is equal to 10 sons. Whatever result you get from 10 sons, The same result one will get it from one daughter alone.
एक पुत्री दस पुत्रों के समान है। कोई व्यक्ति दस पुत्रों के लालन-पालन से जो फल प्राप्त करता है वही फल केवल एक कन्या के पालन-पोषण से प्राप्त हो जाता है।