كتاب المقدمات
1
The Book of Miscellany
Ibn Mas'ud (May Allah be pleased with him) said:
One night I joined the Prophet (ﷺ) in his (optional) Salat. He prolonged the standing so much that I thought of doing something evil. He was asked: "What did you intend to do?" He replied: "To sit down and leave him".

[Al-Bukhari and Muslim].

التاسع‏:‏ عن ابن مسعود رضي الله عنه قال‏:‏ صليت مع النبي صلى الله عليه وسلم ليلة، فأطال القيام حتى هممت بأمر سوء‏!‏ قيل‏:‏ وما هممت به‏؟‏
قال‏:‏ هممت أن أجلس وأدعه‏.‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏
Arabic/English book reference : Book 1, Hadith 103