كتاب المقدمات
1
The Book of Miscellany
Abu Hurairah (May Allah be pleased with him) reported:
Messenger of Allah (ﷺ) said, "A strong believer is better and dearer to Allah than a weak one, and both are good. Adhere to that which is beneficial for you. Keep asking Allah for help and do not refrain from it. If you are afflicted in any way, do not say: 'If I had taken this or that step, it would have resulted into such and such,' but say only: 'Allah so determined and did as He willed.' The word 'if' opens the gates of satanic thoughts".

[Muslim].

السادس‏:‏ عن أبي هريرة رضي الله عنه قال‏:‏ قال رسول الله صلى الله عليه وسلم‏:‏ ‏ "‏ المؤمن القوي خير وأحب إلى الله من المؤمن الضعيف وفي كل خير‏.‏ احرص على ما ينفعك، واستعن بالله ولا تعجز‏.‏ وإن أصابك شيء فلا تقل‏:‏ لو أني فعلت كان كذا وكذا، ولكن قل‏:‏ قدر الله، وما شاء فعل؛ فإن لو تفتح عمل الشيطان‏"‏ ‏(‏‏(‏ رواه مسلم‏)‏‏)‏‏.‏
Arabic/English book reference : Book 1, Hadith 100