Answered by Shaykh Faraz Rabbani
What if I started bowing, then returned to perform the qunut (in witr prayer)?
The place for the qunut supplication is before bowing. Thus:
If one tried to return after having reached the minimum bowing position (such that one’s hands would reach one’s knees), then one missed the proper place for the qunut. Given that the qunut is necessary (wajib), this would require forgetfulness prostrations when performed forgetfully.
If one returns before having reached the minimum bowing position (such that one’s hands wouldn’t reach one’s knees), then nothing is required. [Shurunbulali, Maraqi al-Falah; Ibn Abidin, Radd al-Muhtar]
If unsure, use your reasoned judgment. Our operating assumption and certainty is that we were standing. Unless reasonably sure that one did move into bowing position, one assumes that one was still in standing position. [ibid.]
This relates to five legal maxims:
Certainty is not lifted by doubts.
Rather, certainty is only lifted by certainty.
However, when certainty is not possible, one may rely on reasonable surety.
Reasonable surety must have a reasonable basis.
Reasonable basis is either: relevant past experience; obvious signs; or reliable expert opinion.
[Sources: Majallat al-Ahkam al-Shar`iyya; its Sharh by Allama Ahmad Zarqa; Barkawi, Majami` al-Haqa’iq; Ibn Nujaym, al-Ashbah wa’l Naza’ir; its commentaries by Hamawi and Biri]
And Allah alone gives success.
[Source: QA Forum for Sunni Path Academy course on The Absolute Essentials of Islam, www.SunniPath.com/school]