Al-Kāfi - Volume 4 > Disciplines to Maintain in the State of al-’Ihram
Hadith #4

4ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ مُحَمَّدِ بْنِ الْحُسَيْنِ عَنْ مُحَمَّدِ بْنِ إِسْمَاعِيلَ عَنْ حَمَّادِ بْنِ عِيسَى عَنْ أَبِي عَبْدِ الله (عَلَيْهِ السَّلاَم) قَالَ لَيْسَ لِلْمُحْرِمِ أَنْ يُلَبِّيَ مَنْ دَعَاهُ حَتَّى يَقْضِيَ إِحْرَامَهُ قُلْتُ كَيْفَ يَقُولُ قَالَ يَقُولُ يَا سَعْدُ.

4. Muhammad ibn Yahya has narrated from Muhammad ibn al-Husayn from Muhammad ibn ‘Isma‘il from Hammad ibn ‘Isa who has said the following: “Abu ‘Abd Allah, ‘Alayhi al-Salam, has said, ‘One who is in the state of Ihram must not answer anyone with the world ‘Labbayka’ until Ihram is complete.’ I then asked, ‘How he must say it.’ He (the Imam) said, ‘He can say, ‘O Sa‘d.’”