Nedarim 7a - Safek Matnos Aniyim l'kula

The Ran elaborates to prove that a safeik that arises whether or not one has an obligation to give matnos aniyim, we go l'kula and not l'chumra. Although if we view it as an issur we should say safek d'oraysa l'chumra and the monetary obligation stems from the chiyuv and therefore we would obligate him to give, in reality we view it as a monetary safeik where we pasken that the aniyim have the burden of proof that it belongs to them, so m'safeik there is no obligation to give. The Turei Even in Rosh Hashana 14a regarding the story with R' Akiva who was unsure whether the produce he had was chayev in ma'aser sheini or ma'aser ani (based on a safeik when the rosh hashana l'ilanos is), and was machmir to do both, implying that he actually gave it to the aniyim m'safeik. After some discussion the Turei Even in his avnei miluim says that we are machmir by safeik matnos aniyim.

However, the imrei baruch in his hearos on the Turei Even explains that it depends on the specific type of safeik. If there is a chezkas chiyuv and the safeik is whether some situation arose to exempt him from the obligation then we would say safeik l'chumra, but if the safeik is whether or not he has an obligation altogether then we pasken safeik l'kula like the Ran. We find this concept in other places as well - the shach in y.d. kuntres hasfeikos (110:20) says that one of the limitations of safeik d'rabonon l'kula is that we are not meikil if there is a chezkas issur. Meaning if there is a chezkas issur, then the chazaka paskens to be machmir and we never implement the safek d'rabonon l'kula (the pri chadash argues on shach). Based on this concept, the shach in nekudos hakesef (hilchos melicha siman 69) argues on the Taz (69:24) who paskens that if there is a safeik about a piece of meat whether it was salted, we say safeik d'rabonon l'kula (blood that was cooked is only assur m'drabonon), and the shach argues that since it is 'Ischazek Issura' we have to be machmir. The Binas Adam (29) says that the machlokes shach and taz is dependent on the 2 answers of Tosafos in pesachim 9a.