It was narrated that Ibn ‘Abbás said: “I am surprised at those who anticipate the month, when the Messenger of Allah صلی اللہ علیہ وآلہ وسلم said: ‘When you see the new crescent then fast, and when you see it, then stop fasting, and if it is obscured from you (too cloudy), then complete thirty days.” (Sahih).