And Abraham took his son Yishmael and all those born into his household and those he had acquired - all males of the men of Abraham's house - and he circumcised their foreskins on that very day as God had spoken to him.
And Abraham was ninety-nine years old when he circumcised his foreskin.
It would certainly appear that, despite the obvious difficulties it entailed, Abraham did not hesitate to fulfill God's Will. Nevertheless (as observed by the author of this essay), the midrash in Braishis Rabba 42:8 suggests otherwise:
בשעה שאמר הקב"ה לאברהם לימול, הלך ונמלך בג' אוהביו. אמר לו ענר: כבר בן ק' שנה אתה, ואתה הולך ומצער את עצמך. אמר לו אשכול: מה את הולך ומסיים את עצמך בין שונאיך.אמר לו ממרא: אלהיך שעמד לך: בכבשן האש, ובמלכים, וברעבון, והדבר הזה שאמר לך למול, אין אתה שומע לו.
When the Holy One, Blessed be He, told Abraham to circumcise himself, (Abraham) went and consulted his three friends. Aner said to him: "You are already 100 years old and will you go and cause yourself such suffering?"
Eshkol said to him: "Why would you go to finish yourself [perhaps this means "destroy what standing you still have"] among your enemies?"
Mamre said to him: "Your God who stood for you (saving you) at the burning furnace, (from the four) kings and (during the) famine, and He (now) tells you this thing to circumcise yourself, won't you listen to Him?
The fact that, in the midrash's narrative, Abraham consulted with his friends before performing the circumcision, suggests most strikingly that he wasn't entirely sure what he should do. This doesn't seem at all supported by the enthusiasm portrayed in the Torah itself. So from where did it come? While it's true that the rabbis describe the fulfillment of this mitzva by Abraham as a "test" (that it was, in other words, something difficult for Abraham to do), there really is no definite source proving that he faced internal conflict.
Perhaps, then, the midrash proposes the hypothetical possibility of Abraham's self-doubt to highlight his eventual compliance. In other words, here's the lesson: even if you do sometimes encounter emotional or theological challenges that leave you unsure how to act, don't allow them to overwhelm you and trap you in some endless cycle of moral confusion. Seek help where it is available and then, one way or another, decide. And act.