The Prophet (peace and blessings be upon him) said:
"When any of you is called and he comes along with the messenger, then that (coming along with him) is his permission (to enter)."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 543
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[خد د هب] عن أبي هريرة. الإرواء ١٩٥٥.