Regarding runaways, it’s actually quite pashut. See Devarim 23:16.
The gemara in gittin records a machlokes what this refers to.
The passuk says ?? ????? ??? ?? ?????? ??? ???? ???? ??? ??????
Do not return a slave to his master, who has escaped to you from his master.
??? ??? ???? ????? says this applies where a slave escapes from outside eretz yisroel to eretz yisroel. The braisa says that the slave can force the master to free him, and agree to pay the master his value. Rambam brings this in Avadim 8:10.
??? says that this applies to a person who purchases a slave and stipulates that it is on condition that he will immediately free him. He is therefore required to free him.