Legal imposition of the "rajm" punishment was very rare in Islamic history. During the 623-year history of the Ottoman Empire, for which we have voluminous court records, there is only one recorded example of a judge sentencing a convict to death by stoning, and the ruling contravened Islamic law on at least two grounds (sufficient evidence was not produced, and a Jewish man was sentenced to death despite the law stating clearly that the death penalty for illegal sex should only be applied to Muslims). No sentences of stoning have been recorded in Syria during Muslim rule. Muslim jurists used a number of techniques to avoid application of the stoning penalty. They interpreted the evidentiary requirements so strictly that it was effectively impossible to prove the offense. They actively encouraged witnesses to withhold testimony, and argued that it was morally better to do so. They defined the offense narrowly to exclude many types of sexual activity. And they developed the legal concept of shubha (doubt), which held that when an illegal sexual act resembled legal sex in some way, the stoning penalty should not be applied. Techniques used to argue that the pregnancy of a single woman should not be considered evidence of zināʿ included fantastic presumptions about the length of the human gestation period. Classical Hanafite jurists ruled that it could last for up to two years, Shafi'ites four, and Malikites as long as five years. Rashidun Caliph Umar once acquitted a pregnant single mother on the grounds that she was a "heavy sleeper" who had had "intercourse without realizing it".