Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: I am amazed at those people who begin the month in advance, even though the Prophet (peace and blessings be upon him) said: "Do not fast until you see the moon with your own eyes," or he said: "Fast upon sighting the moon."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 1931
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد فيه عمرو بن دينار مجهول.