Reference for Bava Batra 241:3

אמר ליה מועדי ה' צריכין קידוש בית דין שבת בראשית אינה צריכה קידוש בית דין סלקא דעתך אמינא הואיל וכתיבי גבי מועדות תיבעי קידוש בית דין כמועדות קא משמע לן

require a proclamation by a court<span class="x" onmousemove="('comment',' [H] lit., 'the sanctification of the house of law'. The calendar not having been fixed, the dates of the New Moons and Festivals were determined by the court in Jerusalem on the evidence of witnesses who saw the 'birth', [H] of the new moon. If the court was satisfied, after due investigation and cross-examining of witnesses, that the evidence was reliable, the New Moon, [H] was proclaimed, thus determining also the date of the festival which happened to fall in that month, since the Festivals always occurred, in accordance with the Biblical injunction, on the same day of the respective month. ');">⁶</span> [but] the weekly Sabbath does not require proclamation by a court;<span class="x" onmousemove="('comment',' Sabbath has been divinely ordained and sanctified at the Creation (Gen. II, 3), and is not subject to the proclamation of a human court. ');">⁷</span> for, it might have been assumed, since it<span class="x" onmousemove="('comment',' The Sabbath. ');">⁸</span>

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