同宿文華殿 Lodged In The Hall Of Literary Glory
行者往殿上請師父同至館中製藥。那長老正自起身，忽見內宮傳旨，教閣下留住法師，同宿文華殿。待明朝服藥之後，病痊酬謝，倒換關文送行。行者往殿上请师父同至馆中制药。那长老正自起身，忽见内宫传旨，教阁下留住法师，同宿文华殿。待明朝服药之后，病痊酬谢，倒换关文送行。
逐句解 Line by line
Pilgrim went up to the hall to ask his master to come with him to the hostel and compound the medicine.
He goes to collect his master. In the next sentence the palace gets there first.
The elder was just rising when word came out from the inner palace: the cabinet was to keep the Master of the Law where he was, and lodge him overnight in the Hall of Literary Glory.
The order is dressed as hospitality and phrased so that there is nobody to refuse: the cabinet is to keep the Master of the Law where he is, and put him up for the night in the Hall of Literary Glory. 宿 is sù, to pass the night. 教 is jiào, to have somebody do something.
Once the medicine had been taken the next morning and the sickness cured, there would be thanks and gifts, the travel rescript would be signed over, and they would be seen on their way.
Every clause of the promise is conditional on the king recovering. 朝 is zhāo here, morning — 明朝 is tomorrow — where a moment ago the same character was cháo, the court, in 朝門. 倒換關文 is standard pilgrimage business: every kingdom endorses the travel papers before the party is allowed to leave, so withholding them is a real hold.
Pilgrim comes to collect his master and finds the palace has moved first. The order arrives dressed as hospitality: a night in the Hall of Literary Glory, thanks and gifts to follow, the travel papers signed over, and the party seen on its way.
Every clause of it is conditional on the king getting well, and nothing in the wording admits that a hostage is being taken. That is why Tripitaka has to say it himself in the next breath.