Jesus sent to Lost Sheep of Israel

Matthew 15:

24 He answered, “I was sent only to the lost sheep of Israel.”

Matthew 10:

5 These twelve Jesus sent out, charging them, “Go nowhere among the Gentiles, and enter no town of the Samaritans, 6 but go rather to the lost sheep of the house of Israel. 7 And preach as you go, saying, ‘The kingdom of heaven is at hand.’

It is in Acts 15 that the disciples decide that they should not avoid the Gentiles and should actively preach to them.

Galatians 2:

6 And from those who were reputed to be something (what they were makes no difference to me; God shows no partiality)—those, I say, who were of repute added nothing to me; 7 but on the contrary, when they saw that I had been entrusted with the gospel to the uncircumcised, just as Peter had been entrusted with the gospel to the circumcised 8 (for he who worked through Peter for the mission to the circumcised worked through me also for the Gentiles), 9 and when they perceived the grace that was given to me, James and Cephas and John, who were reputed to be pillars, gave to me and Barnabas the right hand of fellowship, that we should go to the Gentiles and they to the circumcised; 10 only they would have us remember the poor, which very thing I was eager to do.