A ḥadīth in which one rāwī is replaced by another, whether it is one narrator or more, to the extent that is the whole sanad, is termed as maqlūb.[1]
Some have said, maqlūb is that which the name of a narrator is switched with the name of his father.[2]
Qalb (switching of words) sometimes occurs in the matn as well.[3]
[1] This is the definition given by Ibn Ṣalāh and those who followed him. For example the incident of the scholars of Baghdād when they were testing Imām Bukhāri. Literally; turned over, inverted, reversed.
[2] For example switching Murrah ibn Ka’b with Ka’b ibn Murrah. This is the opinion of Ibn Ḥājar.
[3] For example the ḥadīth of ‘Ā’isha from the Prophet ﷺ that he said; “إِنَّ بِلَالًا يُؤَذِّنُ بِلَيْلٍ، فَكُلُوا وَاشْرَبُوا حَتَّى يُؤَذِّنَ ابْنُ أُمِّ مَكْتُومٍ”(Bukhāri 622, Muslim381), however this ḥadīth has also been narrated via a different chain from ‘Ā’isha that the Prophet ﷺ said; “إِنَّ ابْنَ أُمِّ مَكْتُومٍ يُؤَذِّنُ بِلَيْلٍ، فَكُلُوا وَاشْرَبُوا حَتَّى يُؤَذِّنَ بِلَالٌ” (Ṣaḥīḥ Ibn Khuzaymah 406, Ṣaḥīḥ Ibn Ḥibbān 3473). Ibn Ḥājar mentions it is possible that Bilāl and Ibn Umm Maktūm alternated their adhān, thus both ḥadīth would be correct. However, al-Ḍiyā al-Maqdisī rejected this view, and mentions; Ibn ‘Abd al-Barr, Ibn al-Jawzī and al-Mizzī followed them, ruling the narration of Unaysah [i.e. the latter of the two narrations mentioned above] to be a mistake, and that it is maqlūb (summarised from Talkhīs al-Ḥabīr 1/457).
