First, after he hears his brothers express regret for how they treated him:
They did not realize that Joseph was listening, since they [had spoken to him] through a translator. Joseph left them and wept. When he returned, he spoke to them sternly again.
Later, after Joseph sees his younger brother, Benjamin:
Joseph rushed out. His emotions had been aroused by his brother, and he had to weep. He went to a room and there he wept. He washed his face and came out. Holding in his emotions, he said, 'Serve the meal.'
In this week's Ten Minutes of Torah, Rabbi Charles A. Kroloff writes about Joseph's inability to cry in front of others (an inhibition he will overcome next week) and discusses why we shouldn't be afraid to express emotions through tears. Click here to read his commentary.
Moses spoke to the heads of the Israelite tribes, saying: "This is what the Eternal has commanded: If a householder makes a vow to the Eternal or takes an oath imposing an obligation on himself, he shall not break his pledge; he must carry out all that has crossed his lips." - Numbers 30:2-3