Mishnah for Nedarim 84:4
ומי איכא למ"ד ל"ש נכסים אלו ול"ש נכסי והא תנן האומר לחבירו קונם לתוך ביתך שאני נכנס שדך שאני לוקח מת או שמכרו לאחר מותר לבית זה שאני נכנס שדה זו שאני לוקח מת או שמכרו לאחר אסור
They differ [only] in respect of 'My property etc.' Rab and Samuel maintain: There is no difference between 'This property' or 'my property': one can prohibit [for all time]. But R. Johanan and Resh Lakish maintain: [By saying,] 'This property,' he can prohibit; my property,' he cannot prohibit. But does anyone maintain that there is no difference between 'this property' and 'my property'? But we learnt: If one says to his neighbour, 'Konam, if I enter your house,' or 'if I purchase your field,' and then the owner dies or sells it, he is permitted [to enter or buy it]. [But if he says, 'Konam], if I enter this house', or 'if I purchase this field,' and the owner dies or sells it, he is forbidden! — But [explain thus:] R. Johanan and Resh Lakish refer to 'my property'; Rab and Samuel to 'this property': and they do not differ.