According to the Shiva Purana (Rudra Samhita, Parvati Khanda), Mata Parvati performed intense penance (tapasya) for 3,000 years to win Lord Shiva as her consort.
एका पादस्थिता सासीच्छिवं संस्मृत्य पार्वती ।
पंचाक्षरं जपंती च मनुं तेपे तपो महत् ॥ ५० ॥
चीरवल्कलसंवीता जटासंघातधारिणी ।
शिवचिंतनसंसक्ता जिगाय तपसा मुनीम् ॥ ५१ ॥
एवं तस्यास्तपस्यन्त्या चिंतयंत्या महेश्वरम् ।
त्रीणि वर्ष सहस्राणि जग्मुः काल्यास्तपोवने ॥ ५२ ॥50. Then Pārvatī performed great penance standing on one leg and remembering Śiva, she continued muttering the five-syllabled mantra.
51. Clad in barks of trees, wearing matted hair and eager in the meditation of Śiva, she surpassed even sages by her penance.
52. Pārvatī thus spent three thousand years in the penance-grove performing penance and meditating on lord Śiva.
—Shiva Purana,Rudra Samhita, Parvati Khanda, chapter 22