Where is it written that the House must deliver the Articles of Impeachment to the Senate floor before a trial may start in the Senate?
The requirement that the House deliver the Articles of Impeachment is written explicitly in the Senate Rules. It is also implicit in the way the Constitution structures the impeachment process.
The Constitution gives the House the "sole Power of Impeachment," and the Senate the "sole Power to try all Impeachments." To "try an impeachment", the Senate needs an impeachment to "try": No impeachment, no trial. Under the Constitution, an impeachment can only come from the House. In other words, given how the Constitution has divided the power of impeachment and trial, if the Senate doesn't get the articles from the House, they have no case to try.
(The standard analogy may be helpful. Impeachment by the House is usually compared to indictment by a prosecutor. Like an indictment, an impeachment says, "Having looked at the evidence, we charge this person with a crime." Just as in regular trials, the prosecutor does not determine guilt. That is the court's job. In the case of impeachment, the court is the Senate. Its job is to determine whether President is guilty as indicted. Again: No indictment, no trial.)
The need to get the articles of impeachment from the House can be seen in the rules for impeachment trials in the Senate Manual. The Manual devotes 30 pages to "Rules of Procedure and Practice in the Senate when Sitting on Impeachment Trials." The first three rules, detailing the steps that lead to the opening of the trial, all involve the House:
I. Whensoever the Senate shall receive notice from the House of Representatives that managers are appointed on their part to conduct an impeachment against any person and are directed to carry articles of impeachment to the Senate, the Secretary of the Senate shall immediately inform the House of Representatives that the Senate is ready to receive the managers for the purpose of exhibiting such articles of impeachment, agreeably to such notice.
II. When the managers of an impeachment shall be introduced at the bar of the Senate and shall signify that they are ready to exhibit articles of impeachment against any person, the Presiding Officer of the Senate shall direct the Sergeant at Arms to make proclamation, who shall, after making proclamation, repeat the following words, viz: ‘‘All persons are commanded to keep silence, on pain of imprisonment, while the House of Representatives is exhibiting to the Senate of the United States articles of impeachment against ——— ———’’; after which the articles shall be exhibited, and then the Presiding Officer of the Senate shall inform the managers that the Senate will take proper order on the subject of the impeachment, of which due notice shall be given to the House of Representatives.
III. Upon such articles being presented to the Senate, the Senate shall, at 1 o’clock afternoon of the day (Sunday excepted) following such presentation, or sooner if ordered by the Senate, proceed to the consideration of such articles and shall continue in session from day to day (Sundays excepted) after the trial shall commence (unless otherwise ordered by the Senate) until final judgment shall be rendered, and so much longer as may, in its judgment, be needful...
Moreover, the House appoints managers who present the House's case to the Senate. Without them, no trial.