Abdullah bin Amr bin As reported,

I was told that the Messenger of Allah ﷺ said, "A man's prayer while seated is half the prayer."So I came to him and found him praying while sitting. I placed my hand on his head, and he asked, "What is the matter with you, Abdullah bin Amr?"I replied, "Messenger of Allah, I was told that you said, 'A man's prayer while seated is half the prayer,' yet here you are praying while seated."He said, "Yes, but I am not like any of you."

Muslim 1715

Sahih

و حدثني زهير بن حرب حدثنا جرير عن منصور عن هلال بن يساف عن أبي يحيى

عن عبد الله بن عمرو قال

حدثت أن رسول الله ﷺ قال صلاة الرجل قاعدا نصف الصلاة قال فأتيته فوجدته يصلي جالسا فوضعت يدي على رأسه فقال ما لك يا عبد الله بن عمرو قلت حدثت يا رسول الله أنك قلت صلاة الرجل قاعدا على نصف الصلاة وأنت تصلي قاعدا قال أجل ولكني لست كأحد منكم

مسلم 1715صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Travelers' prayer and its shortening
Chapter
Permissibility of voluntary prayer standing and sitting, and performing part of a rakat standing and part sitting
Numbering
Darussalam 1715
Muslim 1715