Praise be to Allah.
The feeding of the infant after the age of six months is one of the matters that are completely governed by custom, and it not a matter of worship. The basic principle with regard to such matters is that they are permissible, and nothing is disallowed unless there is evidence to that effect from Islamic teachings. If there is no such evidence, then the matter remains permissible and allowed. This is the established principle according to Islam.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
People’s actions and words are of two types: acts of worship through which they fulfil their religious duties, and matters of custom and tradition that are connected to their worldly interests.
By studying the fundamentals of Islam, we learn that with regard to the acts of worship that Allah has enjoined or that He loves, matters can only be based on religious texts.
As for matters of custom and tradition, this refers to things that people are accustomed to doing for worldly purposes and serve their worldly interests. In principle, these things are not disallowed, so nothing is to be regarded as being disallowed except that which Allah, may He be glorified and exalted, has forbidden.
The basic principle with regard to customs and traditions is that they are overlooked and permissible, and nothing of them is to be regarded as disallowed except that which the religious texts prohibited. Otherwise, what Allah says about the mushrikeen would be applicable to us: “Say, ‘Have you seen what Allah has sent down to you of provision of which you have made [some] lawful and [some] unlawful?’” [Yoonus 10:59]. Hence Allah criticised the mushrikeen who introduced a religion to which Allah has not consented (cf. 42:21), and they prohibited things that He had not prohibited.… This is a useful and important principle.
End quote from Majmoo‘ al-Fataawa (29/16-18).
Then you should examine the issue of feeding infants, and other similar, permissible customs and traditions. It should be based on what is in the child’s best interests, and other interests. Whatever custom and tradition have shown to be in people’s best interests, on the basis of practice and experience, then people may adopt it and act in accordance with it, as is the case in all their affairs. This is what may be understood from the great principle that the Prophet (blessings and peace of Allah be upon him) taught to his companions: “You know better about your worldly affairs.” Narrated by Muslim (2363).
It is well-known that the infant’s teeth usually begin to appear around the age of six months, and the main function of the teeth is to chew food. This is an indication that at this age, the infant’s body is ready to receive food other than the mother’s milk. So suitable food may be gradually introduced at this age.
Ibn al-Qayyim (may Allah have mercy on him) said:
They (infants) should be restricted to milk only until their teeth begin to appear, because their stomachs are weak and unable to digest food. Once the infant’s teeth begin to appear and his stomach becomes stronger, then he may be nourished with food. Allah, may He be glorified, has delayed the growth of the teeth until the time when the infant needs food, by His wisdom, kindness and mercy towards the mother, so that the child will not bite the breast with his teeth.
Food should be introduced gradually. The first thing that infants should be given is soft food, so they should be given bread that has been soaked in hot water, yoghurt and milk. After that, cooked food and broth without meat may be given; then after that, very soft meat that has been thoroughly chewed or chopped very finely may be introduced.
End quote from Tuhfat al-Mawdood bi Ahkaam al-Mawlood (p. 339).
Moreover, depriving the infant of regular food altogether after he has reached the age of six months may be harmful to him, because his mother’s milk may not be enough for him. Furthermore, he may desire real food after the age of six months, so depriving him of it would be a kind of cruelty and would reflect a lack of compassion for him. Introducing food to him gradually prepares him for weaning, so that when the time comes to wean him, his body will be ready to do without milk, and he will be content with food.
The gradual introduction of food that is suitable for his age has another psychological benefit: it will make it easy for him to be weaned from his mother, when he reaches the age of weaning. This is stated by specialists in psychology. Thus stopping breastfeeding will be done gradually, and that will be kinder to him when breastfeeding comes to an end and he reaches the stage of weaning.
Your husband’s keenness to follow the Sahaabah is something praiseworthy, but this and similar issues have nothing to do with worship, as noted above; rather these matters come under the heading of customs and traditions, and what is in the child’s best interests. So you should not look for evidence from the actions of the Sahaabah regarding such issues; rather you should seek evidence from the actions of the Sahaabah regarding acts of worship.
And Allah knows best.