The Messenger of Allah ﷺ said to me, "Do not slump down between the two prostrations."
حدثنا علي بن محمد حدثنا عبيد الله بن موسى عن إسرائيل عن أبي إسحق عن الحارث
قال لي رسول الله ﷺ لا تقع بين السجدتين
No references are available.
[Its isnad is daif]. Tirmidhi transmitted it in the Book of Prayer, chapter on the dislike of sitting on one's heels between the two prostrations, no. 282, from the hadith of Ubaydullah, through this route. See also no. 95 for its defect.