Is this narration authentic found in "Successors of the Messenger" by Khalid Muhammad Khalid, p. 70:
"Abu Bakr said if I had one By Allah! I would not feel safe from the deception of Allah, even if I had one foot in paradise."
This narration is not found in any of the authentic collections of Hadeeth.
From the answer to this question on IslamQA:
ما يذكره بعض الناس عن أبي بكر رضي الله عنه - ويحكيه بعضهم عن عمر رضي الله عنه – أنه قال : " لو كانت إحدى قدمي في الجنة والأخرى خارجها لما أمنت مكر الله " لم نجد له أصلا في كتب أهل الحديث ، ولا نعلم أحدا من أهل العلم ذكره . وقد سئل عنه الشيخ الألباني رحمه الله فقال : " ما أعرفه " انتهى .
As for the saying that is attributed by some people to Abu Bakr, may Allah be pleased with him, and some attribute it to 'Umar, may Allah be pleased with him:
"If one of my feet were inside Paradise and the other outside it, I would not feel safe from the plan of Allah."
we could not find any basis for this (narration) in the books of the people of Hadeeth, nor did we find any of the scholars make mention of it.
And (when) Shaikh Al-Albaani was asked about it, he said: "I don't know about it."
The translation of the word مكر in this context as "deception" is a poor one. I would suggest using the word plan or plot here in lieu of it.