The last instruction the Messenger of Allah ﷺ gave him before parting was, "When you lead people in prayer, keep it brief." He even specified for me, "Recite Surah Iqra bismi rabbika alladhi khalaq."
حدثنا عفان قال حدثنا وهيب قال حدثنا عبد الله بن عثمان عن داود بن أبي عاصم
أن آخر ما فارقه رسول الله ﷺ قال إذا صليت بقوم فخفف بهم حتى وقت لي اقرأ باسم ربك الذي خلق
Its isnad is sahih. Dawud bin Abu Asim al-Makki is a well-known and reliable narrator. The hadith has already appeared at 17825.